13.5.18

fix #344 - formatting attribute assign bug
add transaction to subdocs event
2021-11-06 14:39:55 +01:00 · 2021-11-06 14:35:04 +01:00 · 2021-11-02 23:24:28 +01:00 · 2021-10-29 22:04:59 +02:00 · 2021-10-29 21:55:55 +02:00 · 2021-10-29 21:53:21 +02:00
99 changed files with 18890 additions and 5564 deletions
--- a/.bowerrc
+++ b/.bowerrc
@@ -1,3 +0,0 @@
-{
- "directory": "../"
-}
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -0,0 +1,7 @@
+version: 2.1
+orbs:
+  node: circleci/node@3.0.0
+workflows:
+  node-tests:
+    jobs:
+      - node/test
--- a/.github/workflows/node.js.yml
+++ b/.github/workflows/node.js.yml
@@ -0,0 +1,29 @@
+# This workflow will do a clean install of node dependencies, build the source code and run tests across different versions of node
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
+
+name: Node.js CI
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [10.x, 12.x, 14.x]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npm run build --if-present
+    - run: npm test
--- a/.github/workflows/nodejs.yml
+++ b/.github/workflows/nodejs.yml
@@ -0,0 +1,31 @@
+# This workflow will do a clean install of node dependencies, build the source code and run tests across different versions of node
+# For more information see: https://help.github.com/actions/language-and-framework-guides/using-nodejs-with-github-actions
+
+name: Node.js CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [10.x, 12.x, 13.x]
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v1
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npm run lint
+    - run: npm run test-extensive
+      env:
+        CI: true
--- a/.gitignore
+++ b/.gitignore
@@ -1,12 +1,4 @@
 node_modules
-bower_components
-build
-build_test
-.directory
-.codio
-.settings
-.jshintignore
-.jshintrc
-.validate.json
-/y.js
-/y.js.map
+dist
+.vscode
+docs
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,4 +0,0 @@
-[submodule "dist"]
-	path = dist
-	url = https://github.com/y-js/yjs.git
-	branch = dist
--- a/.jsdoc.json
+++ b/.jsdoc.json
@@ -0,0 +1,52 @@
+{
+  "sourceType": "module",
+  "tags": {
+    "allowUnknownTags": true,
+    "dictionaries": ["jsdoc"]
+  },
+  "source": {
+    "include": ["./src"],
+    "includePattern": ".js$"
+  },
+  "plugins": [
+    "plugins/markdown"
+  ],
+  "templates": {
+    "referenceTitle": "Yjs",
+    "disableSort": false,
+    "useCollapsibles": true,
+    "collapse": true,
+    "resources": {
+      "yjs.dev": "Website",
+      "docs.yjs.dev": "Docs",
+      "discuss.yjs.dev": "Forum",
+      "https://gitter.im/Yjs/community": "Chat"
+    },
+    "logo": {
+      "url": "https://yjs.dev/images/logo/yjs-512x512.png",
+      "width": "162px",
+      "height": "162px",
+      "link": "/"
+    },
+    "tabNames": {
+      "api": "API",
+      "tutorials": "Examples"
+    },
+    "footerText": "Shared Editing",
+    "css": [
+      "./style.css"
+    ],
+    "default": {
+      "staticFiles": {
+          "include": []
+      }
+    }
+  },
+  "opts": {
+    "destination": "./docs/",
+    "encoding": "utf8",
+    "private": false,
+    "recurse": true,
+    "template": "./node_modules/tui-jsdoc-template"
+  }
+}
--- a/.markdownlint.json
+++ b/.markdownlint.json
@@ -0,0 +1,4 @@
+{
+  "default": true,
+  "no-inline-html": false
+}
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,8 +0,0 @@
-language: node_js
-before_install:
-  - "npm install -g bower"
-node_js:
-  - "0.12"
-branches:
-  only:
-    - master
--- a/Examples/OfflineEditing/index.html
+++ b/Examples/OfflineEditing/index.html
@@ -1,12 +0,0 @@
-<!DOCTYPE html>
-<html>
-<body>
-  <button id="button">Disconnect</button>
-  <h1 id="contenteditable" contentEditable></h1>
-  <textarea style="width:80%;" rows=40 id="textfield"></textarea>
-
-  <script src="../../node_modules/simplewebrtc/simplewebrtc.bundle.js"></script>
-  <script src="../../y.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/Examples/OfflineEditing/index.js
+++ b/Examples/OfflineEditing/index.js
@@ -1,50 +0,0 @@
-/* global Y */
-
-// create a shared object. This function call will return a promise!
-Y({
-  db: {
-    name: 'IndexedDB',
-    namespace: 'offlineEditingDemo'
-  },
-  connector: {
-    name: 'WebRTC',
-    room: 'offlineEditingDemo',
-    debug: true
-  }
-}).then(function (yconfig) {
-  // yconfig holds all the information about the shared object
-  window.yconfig = yconfig
-  // yconfig.root holds the shared element
-  window.y = yconfig.root
-
-  // now we bind the textarea and the contenteditable h1 element
-  // to a shared element
-  var textarea = document.getElementById('textfield')
-  var contenteditable = document.getElementById('contenteditable')
-  yconfig.root.observePath(['text'], function (text) {
-    // every time the 'text' property of the yconfig.root changes,
-    // this function is called. Then we bind it to the html elements
-    if (text != null) {
-      // when the text property is deleted, text may be undefined!
-      // This is why we have to check if text exists..
-      text.bind(textarea)
-      text.bind(contenteditable)
-    }
-  })
-  // create a shared TextBind
-  var textpromise = yconfig.root.get('text')
-  if (textpromise == null) {
-    yconfig.root.set('text', Y.TextBind)
-  }
-  // We also provide a button for disconnecting/reconnecting the shared element
-  var button = document.querySelector('#button')
-  button.onclick = function () {
-    if (button.innerText === 'Disconnect') {
-      yconfig.disconnect()
-      button.innerText = 'Reconnect'
-    } else {
-      yconfig.reconnect()
-      button.innerText = 'Disconnect'
-    }
-  }
-})
--- a/Examples/TextBind/index.html
+++ b/Examples/TextBind/index.html
@@ -1,12 +0,0 @@
-<!DOCTYPE html>
-<html>
-<body>
-  <button id="button">Disconnect</button>
-  <h1 id="contenteditable" contentEditable></h1>
-  <textarea style="width:80%;" rows=40 id="textfield"></textarea>
-
-  <script src="../../node_modules/simplewebrtc/simplewebrtc.bundle.js"></script>
-  <script src="../../y.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/Examples/TextBind/index.js
+++ b/Examples/TextBind/index.js
@@ -1,47 +0,0 @@
-/* global Y */
-
-// create a shared object. This function call will return a promise!
-Y({
-  db: {
-    name: 'Memory'
-  },
-  connector: {
-    name: 'WebRTC',
-    room: 'TextBindDemo',
-    debug: true
-  }
-}).then(function (yconfig) {
-  // yconfig holds all the information about the shared object
-  window.yconfig = yconfig
-  // yconfig.root holds the shared element
-  window.y = yconfig.root
-
-  // now we bind the textarea and the contenteditable h1 element
-  // to a shared element
-  var textarea = document.getElementById('textfield')
-  var contenteditable = document.getElementById('contenteditable')
-  yconfig.root.observePath(['text'], function (text) {
-    // every time the 'text' property of the yconfig.root changes,
-    // this function is called. Then we bind it to the html elements
-    if (text != null) {
-      // when the text property is deleted, text may be undefined!
-      // This is why we have to check if text exists..
-      text.bind(textarea)
-      text.bind(contenteditable)
-    }
-  })
-  // create a shared TextBind
-  yconfig.root.set('text', Y.TextBind)
-
-  // We also provide a button for disconnecting/reconnecting the shared element
-  var button = document.querySelector('#button')
-  button.onclick = function () {
-    if (button.innerText === 'Disconnect') {
-      yconfig.disconnect()
-      button.innerText = 'Reconnect'
-    } else {
-      yconfig.reconnect()
-      button.innerText = 'Disconnect'
-    }
-  }
-})
--- a/INTERNALS.md
+++ b/INTERNALS.md
@@ -0,0 +1,179 @@
+# Yjs Internals
+
+This document roughly explains how Yjs works internally. There is a complete
+walkthrough of the Yjs codebase available as a recording:
+https://youtu.be/0l5XgnQ6rB4
+
+The Yjs CRDT algorithm is described in the [YATA
+paper](https://www.researchgate.net/publication/310212186_Near_Real-Time_Peer-to-Peer_Shared_Editing_on_Extensible_Data_Types)
+from 2016. For an algorithmic view of how it works, the paper is a reasonable
+place to start. There are a handful of small improvements implemented in Yjs
+which aren't described in the paper. The most notable is that items have an
+`originRight` as well as an `origin` property, which improves performance when
+many concurrent inserts happen after the same character.
+
+At its heart, Yjs is a list CRDT. Everything is squeezed into a list in order to
+reuse the CRDT resolution algorithm:
+
+- Arrays are easy - they're lists of arbitrary items.
+- Text is a list of characters, optionally punctuated by formatting markers and
+  embeds for rich text support. Several characters can be wrapped in a single
+linked list `Item` (this is also known as the compound representation of
+CRDTs). More information about this in [this blog
+article](https://blog.kevinjahns.de/are-crdts-suitable-for-shared-editing/).
+- Maps are lists of entries. The last inserted entry for each key is used, and
+  all other duplicates for each key are flagged as deleted.
+
+Each client is assigned a unique *clientID* property on first insert. This is a
+random 53-bit integer (53 bits because that fits in the javascript safe integer
+range).
+
+## List items
+
+Each item in a Yjs list is made up of two objects:
+
+- An `Item` (*src/structs/Item.js*). This is used to relate the item to other
+  adjacent items.
+- An object in the `AbstractType` hierarchy (subclasses of
+  *src/types/AbstractType.js* - eg `YText`). This stores the actual content in
+the Yjs document.
+
+The item and type object pair have a 1-1 mapping. The item's `content` field
+references the AbstractType object and the AbstractType object's `_item` field
+references the item.
+
+Everything inserted in a Yjs document is given a unique ID, formed from a
+*ID(clientID, clock)* pair (also known as a [Lamport
+Timestamp](https://en.wikipedia.org/wiki/Lamport_timestamp)). The clock counts
+up from 0 with the first inserted character or item a client makes. This is
+similar to automerge's operation IDs, but note that the clock is only
+incremented by inserts. Deletes are handled in a very different way (see
+below).
+
+If a run of characters is inserted into a document (eg `"abc"`), the clock will
+be incremented for each character (eg 3 times here). But Yjs will only add a
+single `Item` into the list. This has no effect on the core CRDT algorithm, but
+the optimization dramatically decreases the number of javascript objects
+created during normal text editing. This optimization only applies if the
+characters share the same clientID, they're inserted in order, and all
+characters have either been deleted or all characters are not deleted. The item
+will be split if the run is interrupted for any reason (eg a character in the
+middle of the run is deleted).
+
+When an item is created, it stores a reference to the IDs of the preceeding and
+succeeding item. These are stored in the item's `origin` and `originRight`
+fields, respectively. These are used when peers concurrently insert at the same
+location in a document. Though quite rare in practice, Yjs needs to make sure
+the list items always resolve to the same order on all peers. The actual logic
+is relatively simple - its only a couple dozen lines of code and it lives in
+the `Item#integrate()` method. The YATA paper has much more detail on the this
+algorithm.
+
+### Item Storage
+
+The items themselves are stored in two data structures and a cache:
+
+- The items are stored in a tree of doubly-linked lists in *document order*.
+  Each item has `left` and `right` properties linking to its siblings in the
+document. Items also have a `parent` property to reference their parent in the
+document tree (null at the root). (And you can access an item's children, if
+any, through `item.content`).
+- All items are referenced in *insertion order* inside the struct store
+  (*src/utils/StructStore.js*). This references the list of items inserted by
+for each client, in chronological order. This is used to find an item in the
+tree with a given ID (using a binary search). It is also used to efficiently
+gather the operations a peer is missing during sync (more on this below).
+
+When a local insert happens, Yjs needs to map the insert position in the
+document (eg position 1000) to an ID. With just the linked list, this would
+require a slow O(n) linear scan of the list. But when editing a document, most
+inserts are either at the same position as the last insert, or nearby. To
+improve performance, Yjs stores a cache of the 10 most recently looked up
+insert positions in the document. This is consulted and updated when a position
+is looked up to improve performance in the average case. The cache is updated
+using a heuristic that is still changing (currently, it is updated when a new
+position significantly diverges from existing markers in the cache). Internally
+this is referred to as the skip list / fast search marker.
+
+### Deletions
+
+Deletions in Yjs are treated very differently from insertions. Insertions are
+implemented as a sequential operation based CRDT, but deletions are treated as
+a simpler state based CRDT.
+
+When an item has been deleted by any peer, at any point in history, it is
+flagged as deleted on the item. (Internally Yjs uses the `info` bitfield.) Yjs
+does not record metadata about a deletion:
+
+- No data is kept on *when* an item was deleted, or which user deleted it.
+- The struct store does not contain deletion records
+- The clientID's clock is not incremented
+
+If garbage collection is enabled in Yjs, when an object is deleted its content
+is discarded. If a deleted object contains children (eg a field is deleted in
+an object), the content is replaced with a `GC` object (*src/structs/GC.js*).
+This is a very lightweight structure - it only stores the length of the removed
+content.
+
+Yjs has some special logic to share which content in a document has been
+deleted:
+
+- When a delete happens, as well as marking the item, the deleted IDs are
+  listed locally within the transaction. (See below for more information about
+transactions.) When a transaction has been committed locally, the set of
+deleted items is appended to a transaction's update message.
+- A snapshot (a marked point in time in the Yjs history) is specified using
+  both the set of (clientID, clock) pairs *and* the set of all deleted item
+IDs. The deleted set is O(n), but because deletions usually happen in runs,
+this data set is usually tiny in practice. (The real world editing trace from
+the B4 benchmark document contains 182k inserts and 77k deleted characters. The
+deleted set size in a snapshot is only 4.5Kb).
+
+## Transactions
+
+All updates in Yjs happen within a *transaction*. (Defined in
+*src/utils/Transaction.js*.)
+
+The transaction collects a set of updates to the Yjs document to be applied on
+remote peers atomically. Once a transaction has been committed locally, it
+generates a compressed *update message* which is broadcast to synchronized
+remote peers to notify them of the local change. The update message contains:
+
+- The set of newly inserted items
+- The set of items deleted within the transaction.
+
+## Network protocol
+
+The network protocol is not really a part of Yjs. There are a few relevant
+concepts that can be used to create a custom network protocol:
+
+* `update`: The Yjs document can be encoded to an *update* object that can be
+  parsed to reconstruct the document. Also every change on the document fires
+an incremental document updates that allows clients to sync with each other.
+The update object is an Uint8Array that efficiently encodes `Item` objects and
+the delete set.
+* `state vector`: A state vector defines the know state of each user (a set of
+  tubles `(client, clock)`). This object is also efficiently encoded as a
+Uint8Array.
+
+The client can ask a remote client for missing document updates by sending
+their state vector (often referred to as *sync step 1*). The remote peer can
+compute the missing `Item` objects using the `clocks` of the respective clients
+and compute a minimal update message that reflects all missing updates (sync
+step 2).
+
+An implementation of the syncing process is in
+[y-protocols](https://github.com/yjs/y-protocols).
+
+## Snapshots
+
+A snapshot can be used to restore an old document state. It is a `state vector`
+\+ `delete set`. I client can restore an old document state by iterating through
+the sequence CRDT and ignoring all Items that have an `id.clock >
+stateVector[id.client].clock`. Instead of using `item.deleted` the client will
+use the delete set to find out if an item was deleted or not.
+
+It is not recommended to restore an old document state using snapshots,
+although that would certainly be possible. Instead, the old state should be
+computed by iterating through the newest state and using the additional
+information from the state vector.
--- a/README.md
+++ b/README.md
--- a/1
+++ b/1
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -1,207 +0,0 @@
-/* eslint-env node */
-
-/** Gulp Commands
-
-  gulp command*
-    [--export ModuleType]
-    [--name ModuleName]
-    [--testport TestPort]
-    [--testfiles TestFiles]
-
-  Module name (ModuleName):
-    Compile this to "y.js" (default)
-
-  Supported module types (ModuleType):
-    - amd
-    - amdStrict
-    - common
-    - commonStrict
-    - ignore (default)
-    - system
-    - umd
-    - umdStrict
-
-  Test port (TestPort):
-    Serve the specs on port 8888 (default)
-
-  Test files (TestFiles):
-    Specify which specs to use!
-
-  Commands:
-    - build:deploy
-        Build this library for deployment (es6->es5, minified)
-    - dev:browser
-        Watch the ./src directory.
-        Builds the library on changes.
-        Starts an http-server and serves the test suite on http://127.0.0.1:8888.
-    - dev:node
-        Watch the ./src directory.
-        Builds and specs the library on changes.
-        Usefull to run with node-inspector.
-        `node-debug $(which gulp) dev:node
-    - test:
-        Test this library
-*/
-
-var gulp = require('gulp')
-var sourcemaps = require('gulp-sourcemaps')
-var babel = require('gulp-babel')
-var uglify = require('gulp-uglify')
-var minimist = require('minimist')
-var jasmine = require('gulp-jasmine')
-var jasmineBrowser = require('gulp-jasmine-browser')
-var concat = require('gulp-concat')
-var watch = require('gulp-watch')
-var shell = require('gulp-shell')
-var $ = require('gulp-load-plugins')()
-
-var options = minimist(process.argv.slice(2), {
-  string: ['export', 'name', 'testport', 'testfiles', 'regenerator'],
-  default: {
-    export: 'ignore',
-    name: 'y.js',
-    testport: '8888',
-    testfiles: 'src/**/*.js',
-    regenerator: process.version < 'v0.12'
-  }
-})
-
-var polyfills = [
-  './node_modules/gulp-babel/node_modules/babel-core/node_modules/regenerator/runtime.js'
-]
-
-var concatOrder = [
-  'y.js',
-  'Connector.js',
-  'Database.js',
-  'Transaction.js',
-  'Struct.js',
-  'Utils.js',
-  'Databases/RedBlackTree.js',
-  'Databases/Memory.js',
-  'Databases/IndexedDB.js',
-  'Connectors/Test.js',
-  'Connectors/WebRTC.js',
-  'Types/Array.js',
-  'Types/Map.js',
-  'Types/TextBind.js'
-]
-
-var files = {
-  src: polyfills.concat(concatOrder.map(function (f) {
-    return 'src/' + f
-  })),
-  test: ['build/Helper.spec.js'].concat(concatOrder.map(function (f) {
-    return 'build/' + f
-  }).concat(['build/**/*.spec.js']))
-}
-
-if (options.regenerator) {
-  files.test = polyfills.concat(files.test)
-}
-
-gulp.task('deploy:build', function () {
-  return gulp.src(files.src)
-    .pipe(sourcemaps.init())
-    .pipe(concat('y.js'))
-    .pipe(babel({
-      loose: 'all',
-      modules: 'ignore',
-      experimental: true
-    }))
-    .pipe(uglify())
-    .pipe(sourcemaps.write('.'))
-    .pipe(gulp.dest('.'))
-})
-
-gulp.task('deploy:updateSubmodule', function () {
-  return $.git.updateSubmodule({ args: '--init' })
-})
-
-gulp.task('deploy:copy', function () {
-  return gulp.src(['./y.js', './y.js.map', './README.md', 'package.json', 'LICENSE'])
-    .pipe(gulp.dest('./dist/'))
-})
-
-gulp.task('deploy:bump', function () {
-  return gulp.src('./package.json')
-    .pipe($.bump({type: 'patch'}))
-    .pipe(gulp.dest('./'))
-})
-
-gulp.task('deploy', ['deploy:updateSubmodule', 'deploy:bump', 'deploy:build', 'deploy:copy'], function () {
-  return gulp.src('./package.json', {read: false})
-    .pipe(shell([
-      'echo "Deploying version <%= getVersion(file.path) %>"',
-      'cd ./dist/',
-      'git add -A',
-      'git commit -am "Deploy <%= getVersion(file.path) %>" -n',
-      'git push',
-      'git tag -a v<%= getVersion(file.path) %> -m "Release <%= getVersion(file.path) %>"',
-      'git push origin --tags',
-      'cd ..',
-      'git commit -am "Release <%= getVersion(file.path) %>" -n',
-      'git push'
-    ], {
-      templateData: {
-        getVersion: function (s) {
-          return require(s).version
-        }
-      }
-    }))
-})
-
-gulp.task('build:test', function () {
-  var babelOptions = {
-    loose: 'all',
-    modules: 'ignore',
-    experimental: true
-  }
-  if (!options.regenerator) {
-    babelOptions.blacklist = 'regenerator'
-  }
-  gulp.src(files.src)
-    .pipe(sourcemaps.init())
-    .pipe(concat('y.js'))
-    .pipe(babel(babelOptions))
-    .pipe(sourcemaps.write())
-    .pipe(gulp.dest('.'))
-
-  return gulp.src('src/**/*.js')
-    .pipe(sourcemaps.init())
-    .pipe(babel(babelOptions))
-    .pipe(sourcemaps.write())
-    .pipe(gulp.dest('build'))
-})
-
-gulp.task('dev:node', ['test'], function () {
-  gulp.watch('src/**/*.js', ['test'])
-})
-
-gulp.task('dev:browser', ['build:test'], function () {
-  gulp.watch('src/**/*.js', ['build:test'])
-
-  gulp.src(files.test)
-    .pipe(watch(['build/**/*.js']))
-    .pipe(jasmineBrowser.specRunner())
-    .pipe(jasmineBrowser.server({port: options.testport}))
-})
-
-gulp.task('dev', ['build:test'], function () {
-  gulp.start('dev:browser')
-  gulp.start('dev:node')
-})
-
-gulp.task('test', ['build:test'], function () {
-  var testfiles = files.test
-  if (typeof Promise === 'undefined') {
-    testfiles.concat(['src/polyfills.js'])
-  }
-  return gulp.src(testfiles)
-    .pipe(jasmine({
-      verbose: true,
-      includeStuckTrace: true
-    }))
-})
-
-gulp.task('default', ['test'])
--- a/package-lock.json
+++ b/package-lock.json
--- a/package.json
+++ b/package.json
@@ -1,65 +1,89 @@
 {
  "name": "yjs",
-  "version": "0.6.22",
-  "description": "A framework for real-time p2p shared editing on arbitrary complex data types",
-  "main": "y.js",
-  "scripts": {
-    "test": "node --harmony ./node_modules/.bin/gulp test",
-    "lint": "./node_modules/.bin/standard",
-    "build": "./node_modules/.bin/standard build"
+  "version": "13.5.18",
+  "description": "Shared Editing Library",
+  "main": "./dist/yjs.cjs",
+  "module": "./dist/yjs.mjs",
+  "types": "./dist/src/index.d.ts",
+  "sideEffects": false,
+  "funding": {
+    "type": "GitHub Sponsors ❤",
+    "url": "https://github.com/sponsors/dmonad"
  },
-  "pre-commit": [
-    "lint",
-    "test"
+  "scripts": {
+    "test": "npm run dist && node ./dist/tests.cjs --repetition-time 50",
+    "test-extensive": "npm run lint && npm run dist && node ./dist/tests.cjs --production --repetition-time 10000",
+    "dist": "rm -rf dist && rollup -c && tsc",
+    "watch": "rollup -wc",
+    "lint": "markdownlint README.md && standard && tsc",
+    "docs": "rm -rf docs; jsdoc --configure ./.jsdoc.json --verbose --readme ./README.md --package ./package.json || true",
+    "serve-docs": "npm run docs && http-server ./docs/",
+    "preversion": "npm run lint && PRODUCTION=1 npm run dist && npm run docs && node ./dist/tests.cjs --repetition-time 1000 && test -e dist/src/index.d.ts && test -e dist/yjs.cjs && test -e dist/yjs.cjs",
+    "debug": "concurrently 'http-server -o test.html' 'npm run watch'",
+    "trace-deopt": "clear && rollup -c  && node --trace-deopt dist/test.cjs",
+    "trace-opt": "clear && rollup -c  && node --trace-opt dist/test.cjs",
+    "postinstall": "node ./sponsor-y.js"
+  },
+  "exports": {
+    ".": {
+      "import": "./dist/yjs.mjs",
+      "require": "./dist/yjs.cjs"
+    },
+    "./src/index.js": "./src/index.js",
+    "./tests/testHelper.js": "./tests/testHelper.js",
+    "./package.json": "./package.json"
+  },
+  "files": [
+    "dist/yjs.*",
+    "dist/src",
+    "src",
+    "tests/testHelper.js",
+    "sponsor-y.js"
  ],
+  "dictionaries": {
+    "test": "tests"
+  },
  "standard": {
-    "parser": "babel-eslint",
    "ignore": [
-      "build/**",
-      "./y.js",
-      "./y.js.map"
+      "/dist",
+      "/node_modules",
+      "/docs"
    ]
  },
  "repository": {
    "type": "git",
-    "url": "https://github.com/y-js/yjs.git"
+    "url": "https://github.com/yjs/yjs.git"
  },
  "keywords": [
-    "OT",
-    "Operational Transformation",
-    "collaboration",
-    "synchronization",
-    "ShareJs",
-    "OpenCoweb",
-    "concurrency"
+    "Yjs",
+    "CRDT",
+    "offline",
+    "offline-first",
+    "shared-editing",
+    "concurrency",
+    "collaboration"
  ],
  "author": "Kevin Jahns",
-  "email": "kevin.jahns@rwth-aachen.de",
+  "email": "kevin.jahns@protonmail.com",
  "license": "MIT",
  "bugs": {
-    "url": "https://github.com/y-js/yjs/issues"
+    "url": "https://github.com/yjs/yjs/issues"
+  },
+  "homepage": "https://docs.yjs.dev",
+  "dependencies": {
+    "lib0": "^0.2.42"
  },
-  "homepage": "http://y-js.org",
  "devDependencies": {
-    "babel-eslint": "^4.1.2",
-    "gulp": "^3.9.0",
-    "gulp-babel": "^5.2.1",
-    "gulp-bump": "^1.0.0",
-    "gulp-concat": "^2.6.0",
-    "gulp-filter": "^3.0.1",
-    "gulp-git": "^1.6.0",
-    "gulp-jasmine": "^2.0.1",
-    "gulp-jasmine-browser": "^0.2.3",
-    "gulp-load-plugins": "^1.0.0",
-    "gulp-shell": "^0.5.1",
-    "gulp-sourcemaps": "^1.5.2",
-    "gulp-tag-version": "^1.3.0",
-    "gulp-uglify": "^1.4.1",
-    "gulp-util": "^3.0.6",
-    "gulp-watch": "^4.3.5",
-    "minimist": "^1.2.0",
-    "pre-commit": "^1.1.1",
-    "promise-polyfill": "^2.1.0",
-    "standard": "^5.2.2"
+    "@rollup/plugin-commonjs": "^17.0.0",
+    "@rollup/plugin-node-resolve": "^11.2.1",
+    "concurrently": "^3.6.1",
+    "http-server": "^0.12.3",
+    "jsdoc": "^3.6.7",
+    "markdownlint-cli": "^0.23.2",
+    "rollup": "^2.58.0",
+    "standard": "^16.0.4",
+    "tui-jsdoc-template": "^1.2.2",
+    "typescript": "^4.4.4",
+    "y-protocols": "^1.0.5"
  }
 }
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -0,0 +1,94 @@
+import nodeResolve from '@rollup/plugin-node-resolve'
+import commonjs from '@rollup/plugin-commonjs'
+
+const localImports = process.env.LOCALIMPORTS
+
+const customModules = new Set([
+  'y-websocket',
+  'y-codemirror',
+  'y-ace',
+  'y-textarea',
+  'y-quill',
+  'y-dom',
+  'y-prosemirror'
+])
+/**
+ * @type {Set<any>}
+ */
+const customLibModules = new Set([
+  'lib0',
+  'y-protocols'
+])
+const debugResolve = {
+  resolveId (importee) {
+    if (importee === 'yjs') {
+      return `${process.cwd()}/src/index.js`
+    }
+    if (localImports) {
+      if (customModules.has(importee.split('/')[0])) {
+        return `${process.cwd()}/../${importee}/src/${importee}.js`
+      }
+      if (customLibModules.has(importee.split('/')[0])) {
+        return `${process.cwd()}/../${importee}`
+      }
+    }
+    return null
+  }
+}
+
+export default [{
+  input: './src/index.js',
+  output: {
+    name: 'Y',
+    file: 'dist/yjs.cjs',
+    format: 'cjs',
+    sourcemap: true,
+    paths: path => {
+      if (/^lib0\//.test(path)) {
+        return `lib0/dist/${path.slice(5)}.cjs`
+      }
+      return path
+    }
+  },
+  external: id => /^lib0\//.test(id)
+}, {
+  input: './src/index.js',
+  output: {
+    name: 'Y',
+    file: 'dist/yjs.mjs',
+    format: 'esm',
+    sourcemap: true
+  },
+  external: id => /^lib0\//.test(id)
+}, {
+  input: './tests/index.js',
+  output: {
+    name: 'test',
+    file: 'dist/tests.js',
+    format: 'iife',
+    sourcemap: true
+  },
+  plugins: [
+    debugResolve,
+    nodeResolve({
+      mainFields: ['module', 'browser', 'main']
+    }),
+    commonjs()
+  ]
+}, {
+  input: './tests/index.js',
+  output: {
+    name: 'test',
+    file: 'dist/tests.cjs',
+    format: 'cjs',
+    sourcemap: true
+  },
+  plugins: [
+    debugResolve,
+    nodeResolve({
+      mainFields: ['module', 'main']
+    }),
+    commonjs()
+  ],
+  external: ['isomorphic.js']
+}]
--- a/sponsor-y.js
+++ b/sponsor-y.js
@@ -0,0 +1,12 @@
+
+try {
+  const log = require('lib0/dist/logging.cjs')
+
+  log.print()
+  log.print(log.BOLD, log.GREEN, log.BOLD, 'Thank you for using Yjs ', log.RED, '❤\n')
+  log.print(
+    log.GREY,
+    'The project has grown considerably in the past year. Too much for me to maintain\nin my spare time. Several companies built their products with Yjs.\nYet, this project receives very little funding. Yjs is far from done. I want to\ncreate more awesome extensions and work on the growing number of open issues.\n', log.BOLD, 'Dear user, the future of this project entirely depends on you.\n')
+  log.print(log.BLUE, log.BOLD, 'Please start funding the project now: https://github.com/sponsors/dmonad \n')
+  log.print(log.GREY, '(This message will be removed when I achieved my funding goal)\n\n')
+} catch (e) { }
--- a/src/Connector.js
+++ b/src/Connector.js
@@ -1,328 +0,0 @@
-/* globals Y */
-'use strict'
-
-class AbstractConnector {
-  /*
-    opts contains the following information:
-     role : String Role of this client ("master" or "slave")
-     userId : String Uniquely defines the user.
-     debug: Boolean Whether to print debug messages (optional)
-  */
-  constructor (y, opts) {
-    this.y = y
-    if (opts == null) {
-      opts = {}
-    }
-    if (opts.role == null || opts.role === 'master') {
-      this.role = 'master'
-    } else if (opts.role === 'slave') {
-      this.role = 'slave'
-    } else {
-      throw new Error("Role must be either 'master' or 'slave'!")
-    }
-    this.role = opts.role
-    this.connections = {}
-    this.isSynced = false
-    this.userEventListeners = []
-    this.whenSyncedListeners = []
-    this.currentSyncTarget = null
-    this.syncingClients = []
-    this.forwardToSyncingClients = opts.forwardToSyncingClients !== false
-    this.debug = opts.debug === true
-    this.broadcastedHB = false
-    this.syncStep2 = Promise.resolve()
-  }
-  reconnect () {
-  }
-  disconnect () {
-    this.connections = {}
-    this.isSynced = false
-    this.currentSyncTarget = null
-    this.broadcastedHB = false
-    this.syncingClients = []
-    this.whenSyncedListeners = []
-    return this.y.db.stopGarbageCollector()
-  }
-  setUserId (userId) {
-    this.userId = userId
-    return this.y.db.setUserId(userId)
-  }
-  onUserEvent (f) {
-    this.userEventListeners.push(f)
-  }
-  userLeft (user) {
-    delete this.connections[user]
-    if (user === this.currentSyncTarget) {
-      this.currentSyncTarget = null
-      this.findNextSyncTarget()
-    }
-    this.syncingClients = this.syncingClients.filter(function (cli) {
-      return cli !== user
-    })
-    for (var f of this.userEventListeners) {
-      f({
-        action: 'userLeft',
-        user: user
-      })
-    }
-  }
-  userJoined (user, role) {
-    if (role == null) {
-      throw new Error('You must specify the role of the joined user!')
-    }
-    if (this.connections[user] != null) {
-      throw new Error('This user already joined!')
-    }
-    this.connections[user] = {
-      isSynced: false,
-      role: role
-    }
-    for (var f of this.userEventListeners) {
-      f({
-        action: 'userJoined',
-        user: user,
-        role: role
-      })
-    }
-    if (this.currentSyncTarget == null) {
-      this.findNextSyncTarget()
-    }
-  }
-  // Execute a function _when_ we are connected.
-  // If not connected, wait until connected
-  whenSynced (f) {
-    if (this.isSynced) {
-      f()
-    } else {
-      this.whenSyncedListeners.push(f)
-    }
-  }
-  /*
-
-   returns false, if there is no sync target
-   true otherwise
-  */
-  findNextSyncTarget () {
-    if (this.currentSyncTarget != null || this.isSynced) {
-      return // "The current sync has not finished!"
-    }
-
-    var syncUser = null
-    for (var uid in this.connections) {
-      if (!this.connections[uid].isSynced) {
-        syncUser = uid
-        break
-      }
-    }
-    if (syncUser != null) {
-      var conn = this
-      this.currentSyncTarget = syncUser
-      this.y.db.requestTransaction(function *() {
-        conn.send(syncUser, {
-          type: 'sync step 1',
-          stateSet: yield* this.getStateSet(),
-          deleteSet: yield* this.getDeleteSet()
-        })
-      })
-    } else {
-      this.isSynced = true
-      // call when synced listeners
-      for (var f of this.whenSyncedListeners) {
-        f()
-      }
-      this.whenSyncedListeners = []
-      this.y.db.requestTransaction(function *() {
-        yield* this.garbageCollectAfterSync()
-      })
-    }
-  }
-  send (uid, message) {
-    if (this.debug) {
-      console.log(`send ${this.userId} -> ${uid}: ${message.type}`, m) // eslint-disable-line
-    }
-  }
-  /*
-    You received a raw message, and you know that it is intended for Yjs. Then call this function.
-  */
-  receiveMessage (sender, m) {
-    if (sender === this.userId) {
-      return
-    }
-    if (this.debug) {
-      console.log(`receive ${sender} -> ${this.userId}: ${m.type}`, JSON.parse(JSON.stringify(m))) // eslint-disable-line
-    }
-    if (m.type === 'sync step 1') {
-      // TODO: make transaction, stream the ops
-      let conn = this
-      this.y.db.requestTransaction(function *() {
-        var currentStateSet = yield* this.getStateSet()
-        yield* this.applyDeleteSet(m.deleteSet)
-
-        var ds = yield* this.getDeleteSet()
-        var ops = yield* this.getOperations(m.stateSet)
-        conn.send(sender, {
-          type: 'sync step 2',
-          os: ops,
-          stateSet: currentStateSet,
-          deleteSet: ds
-        })
-        if (this.forwardToSyncingClients) {
-          conn.syncingClients.push(sender)
-          setTimeout(function () {
-            conn.syncingClients = conn.syncingClients.filter(function (cli) {
-              return cli !== sender
-            })
-            conn.send(sender, {
-              type: 'sync done'
-            })
-          }, conn.syncingClientDuration)
-        } else {
-          conn.send(sender, {
-            type: 'sync done'
-          })
-        }
-        conn._setSyncedWith(sender)
-      })
-    } else if (m.type === 'sync step 2') {
-      let conn = this
-      var broadcastHB = !this.broadcastedHB
-      this.broadcastedHB = true
-      var db = this.y.db
-      this.syncStep2 = new Promise(function (resolve) {
-        db.requestTransaction(function * () {
-          yield* this.applyDeleteSet(m.deleteSet)
-          this.store.apply(m.os)
-          db.requestTransaction(function * () {
-            var ops = yield* this.getOperations(m.stateSet)
-            if (ops.length > 0) {
-              m = {
-                type: 'update',
-                ops: ops
-              }
-              if (!broadcastHB) { // TODO: consider to broadcast here..
-                conn.send(sender, m)
-              } else {
-                // broadcast only once!
-                conn.broadcast(m)
-              }
-            }
-            resolve()
-          })
-        })
-      })
-    } else if (m.type === 'sync done') {
-      var self = this
-      this.syncStep2.then(function () {
-        self._setSyncedWith(sender)
-      })
-    } else if (m.type === 'update') {
-      if (this.forwardToSyncingClients) {
-        for (var client of this.syncingClients) {
-          this.send(client, m)
-        }
-      }
-      this.y.db.apply(m.ops)
-    }
-  }
-  _setSyncedWith (user) {
-    var conn = this.connections[user]
-    if (conn != null) {
-      conn.isSynced = true
-    }
-    if (user === this.currentSyncTarget) {
-      this.currentSyncTarget = null
-      this.findNextSyncTarget()
-    }
-  }
-  /*
-    Currently, the HB encodes operations as JSON. For the moment I want to keep it
-    that way. Maybe we support encoding in the HB as XML in the future, but for now I don't want
-    too much overhead. Y is very likely to get changed a lot in the future
-
-    Because we don't want to encode JSON as string (with character escaping, wich makes it pretty much unreadable)
-    we encode the JSON as XML.
-
-    When the HB support encoding as XML, the format should look pretty much like this.
-
-    does not support primitive values as array elements
-    expects an ltx (less than xml) object
-  */
-  parseMessageFromXml (m) {
-    function parseArray (node) {
-      for (var n of node.children) {
-        if (n.getAttribute('isArray') === 'true') {
-          return parseArray(n)
-        } else {
-          return parseObject(n)
-        }
-      }
-    }
-    function parseObject (node) {
-      var json = {}
-      for (var attrName in node.attrs) {
-        var value = node.attrs[attrName]
-        var int = parseInt(value, 10)
-        if (isNaN(int) || ('' + int) !== value) {
-          json[attrName] = value
-        } else {
-          json[attrName] = int
-        }
-      }
-      for (var n in node.children) {
-        var name = n.name
-        if (n.getAttribute('isArray') === 'true') {
-          json[name] = parseArray(n)
-        } else {
-          json[name] = parseObject(n)
-        }
-      }
-      return json
-    }
-    parseObject(m)
-  }
-  /*
-    encode message in xml
-    we use string because Strophe only accepts an "xml-string"..
-    So {a:4,b:{c:5}} will look like
-    <y a="4">
-      <b c="5"></b>
-    </y>
-    m - ltx element
-    json - Object
-  */
-  encodeMessageToXml (msg, obj) {
-    // attributes is optional
-    function encodeObject (m, json) {
-      for (var name in json) {
-        var value = json[name]
-        if (name == null) {
-          // nop
-        } else if (value.constructor === Object) {
-          encodeObject(m.c(name), value)
-        } else if (value.constructor === Array) {
-          encodeArray(m.c(name), value)
-        } else {
-          m.setAttribute(name, value)
-        }
-      }
-    }
-    function encodeArray (m, array) {
-      m.setAttribute('isArray', 'true')
-      for (var e of array) {
-        if (e.constructor === Object) {
-          encodeObject(m.c('array-element'), e)
-        } else {
-          encodeArray(m.c('array-element'), e)
-        }
-      }
-    }
-    if (obj.constructor === Object) {
-      encodeObject(msg.c('y', { xmlns: 'http://y.ninja/connector-stanza' }), obj)
-    } else if (obj.constructor === Array) {
-      encodeArray(msg.c('y', { xmlns: 'http://y.ninja/connector-stanza' }), obj)
-    } else {
-      throw new Error("I can't encode this json!")
-    }
-  }
-}
-Y.AbstractConnector = AbstractConnector
--- a/src/Connectors/Test.js
+++ b/src/Connectors/Test.js
@@ -1,136 +0,0 @@
-/* global getRandom, Y, wait, async */
-'use strict'
-
-var globalRoom = {
-  users: {},
-  buffers: {},
-  removeUser: function (user) {
-    for (var i in this.users) {
-      this.users[i].userLeft(user)
-    }
-    delete this.users[user]
-    delete this.buffers[user]
-  },
-  addUser: function (connector) {
-    this.users[connector.userId] = connector
-    this.buffers[connector.userId] = []
-    for (var uname in this.users) {
-      if (uname !== connector.userId) {
-        var u = this.users[uname]
-        u.userJoined(connector.userId, 'master')
-        connector.userJoined(u.userId, 'master')
-      }
-    }
-  }
-}
-Y.utils.globalRoom = globalRoom
-
-function flushOne () {
-  var bufs = []
-  for (var i in globalRoom.buffers) {
-    if (globalRoom.buffers[i].length > 0) {
-      bufs.push(i)
-    }
-  }
-  if (bufs.length > 0) {
-    var userId = getRandom(bufs)
-    var m = globalRoom.buffers[userId].shift()
-    var user = globalRoom.users[userId]
-    user.receiveMessage(m[0], m[1])
-    return true
-  } else {
-    return false
-  }
-}
-
-// setInterval(flushOne, 10)
-
-var userIdCounter = 0
-
-class Test extends Y.AbstractConnector {
-  constructor (y, options) {
-    if (options === undefined) {
-      throw new Error('Options must not be undefined!')
-    }
-    options.role = 'master'
-    options.forwardToSyncingClients = false
-    super(y, options)
-    this.setUserId((userIdCounter++) + '').then(() => {
-      globalRoom.addUser(this)
-    })
-    this.globalRoom = globalRoom
-    this.syncingClientDuration = 0
-  }
-  receiveMessage (sender, m) {
-    super.receiveMessage(sender, JSON.parse(JSON.stringify(m)))
-  }
-  send (userId, message) {
-    var buffer = globalRoom.buffers[userId]
-    if (buffer != null) {
-      buffer.push(JSON.parse(JSON.stringify([this.userId, message])))
-    }
-  }
-  broadcast (message) {
-    for (var key in globalRoom.buffers) {
-      globalRoom.buffers[key].push(JSON.parse(JSON.stringify([this.userId, message])))
-    }
-  }
-  isDisconnected () {
-    return globalRoom.users[this.userId] == null
-  }
-  reconnect () {
-    if (this.isDisconnected()) {
-      globalRoom.addUser(this)
-      super.reconnect()
-    }
-    return this.flushAll()
-  }
-  disconnect () {
-    if (!this.isDisconnected()) {
-      globalRoom.removeUser(this.userId)
-      super.disconnect()
-    }
-    return wait()
-  }
-  flush () {
-    var self = this
-    return async(function * () {
-      yield wait()
-      while (globalRoom.buffers[self.userId].length > 0) {
-        var m = globalRoom.buffers[self.userId].shift()
-        this.receiveMessage(m[0], m[1])
-        yield wait()
-      }
-    })
-  }
-  flushAll () {
-    return new Promise(function (resolve) {
-      // flushes may result in more created operations,
-      // flush until there is nothing more to flush
-      function nextFlush () {
-        var c = flushOne()
-        if (c) {
-          while (flushOne()) {
-            // nop
-          }
-          wait().then(nextFlush)
-        } else {
-          wait().then(function () {
-            resolve()
-          })
-        }
-      }
-      // in the case that there are
-      // still actions that want to be performed
-      wait().then(nextFlush)
-    })
-  }
-  /*
-    Flushes an operation for some user..
-  */
-  flushOne () {
-    flushOne()
-  }
-}
-
-Y.Test = Test
--- a/src/Connectors/WebRTC.js
+++ b/src/Connectors/WebRTC.js
@@ -1,94 +0,0 @@
-/* global Y, SimpleWebRTC */
-'use strict'
-
-class WebRTC extends Y.AbstractConnector {
-  constructor (y, options) {
-    if (options === undefined) {
-      throw new Error('Options must not be undefined!')
-    }
-    if (options.room == null) {
-      throw new Error('You must define a room name!')
-    }
-    options.role = 'slave'
-    super(y, options)
-    this.webrtcOptions = {
-      url: options.url || 'https://yatta.ninja:8888',
-      room: options.room
-    }
-    var swr = new SimpleWebRTC(this.webrtcOptions)
-    this.swr = swr
-    var self = this
-    swr.once('connectionReady', function (userId) {
-      // SimpleWebRTC (swr) is initialized
-      swr.joinRoom(self.webrtcOptions.room)
-
-      swr.once('joinedRoom', function () {
-        self.setUserId(userId)
-        /*
-        var i
-        // notify the connector class about all the users that already
-        // joined the session
-        for(i in self.swr.webrtc.peers){
-          self.userJoined(self.swr.webrtc.peers[i].id, "master")
-        }*/
-        swr.on('channelMessage', function (peer, room_, message) {
-          // The client received a message
-          // Check if the connector is already initialized,
-          // only then forward the message to the connector class
-          if (message.type != null) {
-            self.receiveMessage(peer.id, message.payload)
-          }
-        })
-      })
-
-      swr.on('createdPeer', function (peer) {
-        // a new peer/client joined the session.
-        // Notify the connector class, if the connector
-        // is already initialized
-        self.userJoined(peer.id, 'master')
-      })
-
-      swr.on('peerStreamRemoved', function (peer) {
-        // a client left the session.
-        // Notify the connector class, if the connector
-        // is already initialized
-        self.userLeft(peer.id)
-      })
-    })
-  }
-  disconnect () {
-    this.swr.leaveRoom()
-    super.disconnect()
-  }
-  reconnect () {
-    this.swr.joinRoom(this.webrtcOptions.room)
-    super.reconnect()
-  }
-  send (uid, message) {
-    var self = this
-    // we have to make sure that the message is sent under all circumstances
-    var send = function () {
-      // check if the clients still exists
-      var peer = self.swr.webrtc.getPeers(uid)[0]
-      var success
-      if (peer) {
-        // success is true, if the message is successfully sent
-        success = peer.sendDirectly('simplewebrtc', 'yjs', message)
-      }
-      if (!success) {
-        // resend the message if it didn't work
-        setTimeout(send, 500)
-      }
-    }
-    // try to send the message
-    send()
-  }
-  broadcast (message) {
-    this.swr.sendDirectlyToAll('simplewebrtc', 'yjs', message)
-  }
-  isDisconnected () {
-    return false
-  }
-}
-
-Y.WebRTC = WebRTC
--- a/src/Database.js
+++ b/src/Database.js
@@ -1,341 +0,0 @@
-/* global Y */
-'use strict'
-
-/*
-  Partial definition of an OperationStore.
-  TODO: name it Database, operation store only holds operations.
-
-  A database definition must alse define the following methods:
-  * logTable() (optional)
-    - show relevant information information in a table
-  * requestTransaction(makeGen)
-    - request a transaction
-  * destroy()
-    - destroy the database
-*/
-class AbstractDatabase {
-  constructor (y, opts) {
-    this.y = y
-    // E.g. this.listenersById[id] : Array<Listener>
-    this.listenersById = {}
-    // Execute the next time a transaction is requested
-    this.listenersByIdExecuteNow = []
-    // A transaction is requested
-    this.listenersByIdRequestPending = false
-    /* To make things more clear, the following naming conventions:
-       * ls : we put this.listenersById on ls
-       * l : Array<Listener>
-       * id : Id (can't use as property name)
-       * sid : String (converted from id via JSON.stringify
-                       so we can use it as a property name)
-
-      Always remember to first overwrite
-      a property before you iterate over it!
-    */
-    // TODO: Use ES7 Weak Maps. This way types that are no longer user,
-    // wont be kept in memory.
-    this.initializedTypes = {}
-    this.whenUserIdSetListener = null
-    this.waitingTransactions = []
-    this.transactionInProgress = false
-    if (typeof YConcurrency_TestingMode !== 'undefined') {
-      this.executeOrder = []
-    }
-    this.gc1 = [] // first stage
-    this.gc2 = [] // second stage -> after that, remove the op
-    this.gcTimeout = opts.gcTimeout || 5000
-    var os = this
-    function garbageCollect () {
-      return new Promise((resolve) => {
-        os.requestTransaction(function * () {
-          if (os.y.connector != null && os.y.connector.isSynced) {
-            for (var i in os.gc2) {
-              var oid = os.gc2[i]
-              yield* this.garbageCollectOperation(oid)
-            }
-            os.gc2 = os.gc1
-            os.gc1 = []
-          }
-          if (os.gcTimeout > 0) {
-            os.gcInterval = setTimeout(garbageCollect, os.gcTimeout)
-          }
-          resolve()
-        })
-      })
-    }
-    this.garbageCollect = garbageCollect
-    if (this.gcTimeout > 0) {
-      garbageCollect()
-    }
-  }
-  addToDebug () {
-    if (typeof YConcurrency_TestingMode !== 'undefined') {
-      var command = Array.prototype.map.call(arguments, function (s) {
-        if (typeof s === 'string') {
-          return s
-        } else {
-          return JSON.stringify(s)
-        }
-      }).join('').replace(/"/g, "'").replace(/,/g, ', ').replace(/:/g, ': ')
-      this.executeOrder.push(command)
-    }
-  }
-  getDebugData () {
-    console.log(this.executeOrder.join('\n'))
-  }
-  stopGarbageCollector () {
-    var self = this
-    return new Promise(function (resolve) {
-      self.requestTransaction(function * () {
-        var ungc = self.gc1.concat(self.gc2)
-        self.gc1 = []
-        self.gc2 = []
-        for (var i in ungc) {
-          var op = yield* this.getOperation(ungc[i])
-          delete op.gc
-          yield* this.setOperation(op)
-        }
-        resolve()
-      })
-    })
-  }
-  /*
-    Try to add to GC.
-
-    TODO: rename this function
-
-    Rulez:
-    * Only gc if this user is online
-    * The most left element in a list must not be gc'd.
-      => There is at least one element in the list
-
-    returns true iff op was added to GC
-  */
-  addToGarbageCollector (op, left) {
-    if (
-      op.gc == null &&
-      op.deleted === true &&
-      this.y.connector.isSynced &&
-      left != null &&
-      left.deleted === true
-    ) {
-      op.gc = true
-      this.gc1.push(op.id)
-      return true
-    } else {
-      return false
-    }
-  }
-  removeFromGarbageCollector (op) {
-    function filter (o) {
-      return !Y.utils.compareIds(o, op.id)
-    }
-    this.gc1 = this.gc1.filter(filter)
-    this.gc2 = this.gc2.filter(filter)
-    delete op.gc
-  }
-  destroy () {
-    clearInterval(this.gcInterval)
-    this.gcInterval = null
-  }
-  setUserId (userId) {
-    var self = this
-    return new Promise(function (resolve) {
-      self.requestTransaction(function * () {
-        self.userId = userId
-        self.opClock = (yield* this.getState(userId)).clock
-        if (self.whenUserIdSetListener != null) {
-          self.whenUserIdSetListener()
-          self.whenUserIdSetListener = null
-        }
-        resolve()
-      })
-    })
-  }
-  whenUserIdSet (f) {
-    if (this.userId != null) {
-      f()
-    } else {
-      this.whenUserIdSetListener = f
-    }
-  }
-  getNextOpId () {
-    if (this.userId == null) {
-      throw new Error('OperationStore not yet initialized!')
-    }
-    return [this.userId, this.opClock++]
-  }
-  /*
-    Apply a list of operations.
-
-    * get a transaction
-    * check whether all Struct.*.requiredOps are in the OS
-    * check if it is an expected op (otherwise wait for it)
-    * check if was deleted, apply a delete operation after op was applied
-  */
-  apply (ops) {
-    for (var key in ops) {
-      var o = ops[key]
-      var required = Y.Struct[o.struct].requiredOps(o)
-      this.whenOperationsExist(required, o)
-    }
-  }
-  /*
-    op is executed as soon as every operation requested is available.
-    Note that Transaction can (and should) buffer requests.
-  */
-  whenOperationsExist (ids, op) {
-    if (ids.length > 0) {
-      let listener = {
-        op: op,
-        missing: ids.length
-      }
-
-      for (let key in ids) {
-        let id = ids[key]
-        let sid = JSON.stringify(id)
-        let l = this.listenersById[sid]
-        if (l == null) {
-          l = []
-          this.listenersById[sid] = l
-        }
-        l.push(listener)
-      }
-    } else {
-      this.listenersByIdExecuteNow.push({
-        op: op
-      })
-    }
-
-    if (this.listenersByIdRequestPending) {
-      return
-    }
-
-    this.listenersByIdRequestPending = true
-    var store = this
-
-    this.requestTransaction(function * () {
-      var exeNow = store.listenersByIdExecuteNow
-      store.listenersByIdExecuteNow = []
-
-      var ls = store.listenersById
-      store.listenersById = {}
-
-      store.listenersByIdRequestPending = false
-
-      for (let key in exeNow) {
-        let o = exeNow[key].op
-        yield* store.tryExecute.call(this, o)
-      }
-
-      for (var sid in ls) {
-        var l = ls[sid]
-        var id = JSON.parse(sid)
-        if ((yield* this.getOperation(id)) == null) {
-          store.listenersById[sid] = l
-        } else {
-          for (let key in l) {
-            let listener = l[key]
-            let o = listener.op
-            if (--listener.missing === 0) {
-              yield* store.tryExecute.call(this, o)
-            }
-          }
-        }
-      }
-    })
-  }
-  /*
-    Actually execute an operation, when all expected operations are available.
-  */
-  * tryExecute (op) {
-    this.store.addToDebug('yield* this.store.tryExecute.call(this, ', JSON.stringify(op), ')')
-    if (op.struct === 'Delete') {
-      yield* Y.Struct.Delete.execute.call(this, op)
-      yield* this.store.operationAdded(this, op)
-    } else if ((yield* this.getOperation(op.id)) == null && !(yield* this.isGarbageCollected(op.id))) {
-      yield* Y.Struct[op.struct].execute.call(this, op)
-      yield* this.addOperation(op)
-      yield* this.store.operationAdded(this, op)
-    }
-  }
-  // called by a transaction when an operation is added
-  * operationAdded (transaction, op) {
-    if (op.struct === 'Delete') {
-      var target = yield* transaction.getOperation(op.target)
-      if (target != null) {
-        var type = transaction.store.initializedTypes[JSON.stringify(target.parent)]
-        if (type != null) {
-          yield* type._changed(transaction, {
-            struct: 'Delete',
-            target: op.target
-          })
-        }
-      }
-    } else {
-      // increase SS
-      var o = op
-      var state = yield* transaction.getState(op.id[0])
-      while (o != null && o.id[1] === state.clock && op.id[0] === o.id[0]) {
-        // either its a new operation (1. case), or it is an operation that was deleted, but is not yet in the OS
-        state.clock++
-        yield* transaction.checkDeleteStoreForState(state)
-        o = yield* transaction.os.findNext(o.id)
-      }
-      yield* transaction.setState(state)
-
-      // notify whenOperation listeners (by id)
-      var sid = JSON.stringify(op.id)
-      var l = this.listenersById[sid]
-      delete this.listenersById[sid]
-
-      if (l != null) {
-        for (var key in l) {
-          var listener = l[key]
-          if (--listener.missing === 0) {
-            this.whenOperationsExist([], listener.op)
-          }
-        }
-      }
-      var t = this.initializedTypes[JSON.stringify(op.parent)]
-      // notify parent, if it has been initialized as a custom type
-      if (t != null) {
-        yield* t._changed(transaction, Y.utils.copyObject(op))
-      }
-
-      // Delete if DS says this is actually deleted
-      if (!op.deleted && (yield* transaction.isDeleted(op.id))) {
-        var delop = {
-          struct: 'Delete',
-          target: op.id
-        }
-        yield* Y.Struct['Delete'].execute.call(transaction, delop)
-        if (t != null) {
-          yield* t._changed(transaction, delop)
-        }
-      }
-    }
-  }
-  getNextRequest () {
-    if (this.waitingTransactions.length === 0) {
-      this.transactionInProgress = false
-      return null
-    } else {
-      return this.waitingTransactions.shift()
-    }
-  }
-  requestTransaction (makeGen, callImmediately) {
-    if (callImmediately) {
-      this.transact(makeGen)
-    } else if (!this.transactionInProgress) {
-      this.transactionInProgress = true
-      var self = this
-      setTimeout(function () {
-        self.transact(makeGen)
-      }, 0)
-    } else {
-      this.waitingTransactions.push(makeGen)
-    }
-  }
-}
-Y.AbstractDatabase = AbstractDatabase
--- a/src/Database.spec.js
+++ b/src/Database.spec.js
@@ -1,351 +0,0 @@
-/* global Y, async, databases */
-/* eslint-env browser,jasmine,console */
-
-for (let database of databases) {
-  describe(`Database (${database})`, function () {
-    var store
-    describe('DeleteStore', function () {
-      describe('Basic', function () {
-        beforeEach(function () {
-          store = new Y[database](null, {
-            gcTimeout: -1,
-            namespace: 'testing'
-          })
-        })
-        afterEach(function (done) {
-          store.requestTransaction(function * () {
-            yield* this.store.destroy()
-            done()
-          })
-        })
-        it('Deleted operation is deleted', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['u1', 10])
-            expect(yield* this.isDeleted(['u1', 10])).toBeTruthy()
-            expect(yield* this.getDeleteSet()).toEqual({'u1': [[10, 1, false]]})
-            done()
-          })
-        }))
-        it('Deleted operation extends other deleted operation', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['u1', 10])
-            yield* this.markDeleted(['u1', 11])
-            expect(yield* this.isDeleted(['u1', 10])).toBeTruthy()
-            expect(yield* this.isDeleted(['u1', 11])).toBeTruthy()
-            expect(yield* this.getDeleteSet()).toEqual({'u1': [[10, 2, false]]})
-            done()
-          })
-        }))
-        it('Deleted operation extends other deleted operation', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['0', 3])
-            yield* this.markDeleted(['0', 4])
-            yield* this.markDeleted(['0', 2])
-            expect(yield* this.getDeleteSet()).toEqual({'0': [[2, 3, false]]})
-            done()
-          })
-        }))
-        it('Debug #1', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['166', 0])
-            yield* this.markDeleted(['166', 2])
-            yield* this.markDeleted(['166', 0])
-            yield* this.markDeleted(['166', 2])
-            yield* this.markGarbageCollected(['166', 2])
-            yield* this.markDeleted(['166', 1])
-            yield* this.markDeleted(['166', 3])
-            yield* this.markGarbageCollected(['166', 3])
-            yield* this.markDeleted(['166', 0])
-            expect(yield* this.getDeleteSet()).toEqual({'166': [[0, 2, false], [2, 2, true]]})
-            done()
-          })
-        }))
-        it('Debug #2', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['293', 0])
-            yield* this.markDeleted(['291', 2])
-            yield* this.markDeleted(['291', 2])
-            yield* this.markGarbageCollected(['293', 0])
-            yield* this.markDeleted(['293', 1])
-            yield* this.markGarbageCollected(['291', 2])
-            expect(yield* this.getDeleteSet()).toEqual({'291': [[2, 1, true]], '293': [[0, 1, true], [1, 1, false]]})
-            done()
-          })
-        }))
-        it('Debug #3', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['581', 0])
-            yield* this.markDeleted(['581', 1])
-            yield* this.markDeleted(['580', 0])
-            yield* this.markDeleted(['580', 0])
-            yield* this.markGarbageCollected(['581', 0])
-            yield* this.markDeleted(['581', 2])
-            yield* this.markDeleted(['580', 1])
-            yield* this.markDeleted(['580', 2])
-            yield* this.markDeleted(['580', 1])
-            yield* this.markDeleted(['580', 2])
-            yield* this.markGarbageCollected(['581', 2])
-            yield* this.markGarbageCollected(['581', 1])
-            yield* this.markGarbageCollected(['580', 1])
-            expect(yield* this.getDeleteSet()).toEqual({'580': [[0, 1, false], [1, 1, true], [2, 1, false]], '581': [[0, 3, true]]})
-            done()
-          })
-        }))
-        it('Debug #4', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['544', 0])
-            yield* this.markDeleted(['543', 2])
-            yield* this.markDeleted(['544', 0])
-            yield* this.markDeleted(['543', 2])
-            yield* this.markGarbageCollected(['544', 0])
-            yield* this.markDeleted(['545', 1])
-            yield* this.markDeleted(['543', 4])
-            yield* this.markDeleted(['543', 3])
-            yield* this.markDeleted(['544', 1])
-            yield* this.markDeleted(['544', 2])
-            yield* this.markDeleted(['544', 1])
-            yield* this.markDeleted(['544', 2])
-            yield* this.markGarbageCollected(['543', 2])
-            yield* this.markGarbageCollected(['543', 4])
-            yield* this.markGarbageCollected(['544', 2])
-            yield* this.markGarbageCollected(['543', 3])
-            expect(yield* this.getDeleteSet()).toEqual({'543': [[2, 3, true]], '544': [[0, 1, true], [1, 1, false], [2, 1, true]], '545': [[1, 1, false]]})
-            done()
-          })
-        }))
-        it('Debug #5', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.applyDeleteSet({'16': [[1, 2, false]], '17': [[0, 1, true], [1, 3, false]]})
-            expect(yield* this.getDeleteSet()).toEqual({'16': [[1, 2, false]], '17': [[0, 1, true], [1, 3, false]]})
-            yield* this.applyDeleteSet({'16': [[1, 2, false]], '17': [[0, 4, true]]})
-            expect(yield* this.getDeleteSet()).toEqual({'16': [[1, 2, false]], '17': [[0, 4, true]]})
-            done()
-          })
-        }))
-        it('Debug #6', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.applyDeleteSet({'40': [[0, 3, false]]})
-            expect(yield* this.getDeleteSet()).toEqual({'40': [[0, 3, false]]})
-            yield* this.applyDeleteSet({'39': [[2, 2, false]], '40': [[0, 1, true], [1, 2, false]], '41': [[2, 1, false]]})
-            expect(yield* this.getDeleteSet()).toEqual({'39': [[2, 2, false]], '40': [[0, 1, true], [1, 2, false]], '41': [[2, 1, false]]})
-            done()
-          })
-        }))
-        it('Debug #7', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield* this.markDeleted(['9', 2])
-            yield* this.markDeleted(['11', 2])
-            yield* this.markDeleted(['11', 4])
-            yield* this.markDeleted(['11', 1])
-            yield* this.markDeleted(['9', 4])
-            yield* this.markDeleted(['10', 0])
-            yield* this.markGarbageCollected(['11', 2])
-            yield* this.markDeleted(['11', 2])
-            yield* this.markGarbageCollected(['11', 3])
-            yield* this.markDeleted(['11', 3])
-            yield* this.markDeleted(['11', 3])
-            yield* this.markDeleted(['9', 4])
-            yield* this.markDeleted(['10', 0])
-            yield* this.markGarbageCollected(['11', 1])
-            yield* this.markDeleted(['11', 1])
-            expect(yield* this.getDeleteSet()).toEqual({'9': [[2, 1, false], [4, 1, false]], '10': [[0, 1, false]], '11': [[1, 3, true], [4, 1, false]]})
-            done()
-          })
-        }))
-      })
-    })
-    describe('OperationStore', function () {
-      describe('Basic Tests', function () {
-        beforeEach(function () {
-          store = new Y[database](null, {
-            gcTimeout: -1,
-            namespace: 'testing'
-          })
-        })
-        afterEach(function (done) {
-          store.requestTransaction(function * () {
-            yield* this.store.destroy()
-            done()
-          })
-        })
-        it('debug #1', function (done) {
-          store.requestTransaction(function * () {
-            yield* this.os.put({id: [2]})
-            yield* this.os.put({id: [0]})
-            yield* this.os.delete([2])
-            yield* this.os.put({id: [1]})
-            expect(yield* this.os.find([0])).toBeTruthy()
-            expect(yield* this.os.find([1])).toBeTruthy()
-            expect(yield* this.os.find([2])).toBeFalsy()
-            done()
-          })
-        })
-        it('can add&retrieve 5 elements', function (done) {
-          store.requestTransaction(function * () {
-            yield* this.os.put({val: 'four', id: [4]})
-            yield* this.os.put({val: 'one', id: [1]})
-            yield* this.os.put({val: 'three', id: [3]})
-            yield* this.os.put({val: 'two', id: [2]})
-            yield* this.os.put({val: 'five', id: [5]})
-            expect((yield* this.os.find([1])).val).toEqual('one')
-            expect((yield* this.os.find([2])).val).toEqual('two')
-            expect((yield* this.os.find([3])).val).toEqual('three')
-            expect((yield* this.os.find([4])).val).toEqual('four')
-            expect((yield* this.os.find([5])).val).toEqual('five')
-            done()
-          })
-        })
-        it('5 elements do not exist anymore after deleting them', function (done) {
-          store.requestTransaction(function * () {
-            yield* this.os.put({val: 'four', id: [4]})
-            yield* this.os.put({val: 'one', id: [1]})
-            yield* this.os.put({val: 'three', id: [3]})
-            yield* this.os.put({val: 'two', id: [2]})
-            yield* this.os.put({val: 'five', id: [5]})
-            yield* this.os.delete([4])
-            expect(yield* this.os.find([4])).not.toBeTruthy()
-            yield* this.os.delete([3])
-            expect(yield* this.os.find([3])).not.toBeTruthy()
-            yield* this.os.delete([2])
-            expect(yield* this.os.find([2])).not.toBeTruthy()
-            yield* this.os.delete([1])
-            expect(yield* this.os.find([1])).not.toBeTruthy()
-            yield* this.os.delete([5])
-            expect(yield* this.os.find([5])).not.toBeTruthy()
-            done()
-          })
-        })
-      })
-      var numberOfOSTests = 1000
-      describe(`Random Tests - after adding&deleting (0.8/0.2) ${numberOfOSTests} times`, function () {
-        var elements = []
-        beforeAll(function (done) {
-          store = new Y[database](null, {
-            gcTimeout: -1,
-            namespace: 'testing'
-          })
-          store.requestTransaction(function * () {
-            for (var i = 0; i < numberOfOSTests; i++) {
-              var r = Math.random()
-              if (r < 0.8) {
-                var obj = [Math.floor(Math.random() * numberOfOSTests * 10000)]
-                if (!(yield* this.os.find(obj))) {
-                  elements.push(obj)
-                  yield* this.os.put({id: obj})
-                }
-              } else if (elements.length > 0) {
-                var elemid = Math.floor(Math.random() * elements.length)
-                var elem = elements[elemid]
-                elements = elements.filter(function (e) {
-                  return !Y.utils.compareIds(e, elem)
-                })
-                yield* this.os.delete(elem)
-              }
-            }
-            done()
-          })
-        })
-        afterAll(function (done) {
-          store.requestTransaction(function * () {
-            yield* this.store.destroy()
-            done()
-          })
-        })
-        it('can find every object', function (done) {
-          store.requestTransaction(function * () {
-            for (var id of elements) {
-              expect((yield* this.os.find(id)).id).toEqual(id)
-            }
-            done()
-          })
-        })
-
-        it('can find every object with lower bound search', function (done) {
-          store.requestTransaction(function * () {
-            for (var id of elements) {
-              var e = yield* this.os.findWithLowerBound(id)
-              expect(e.id).toEqual(id)
-            }
-            done()
-          })
-        })
-
-        it('iterating over a tree with lower bound yields the right amount of results', function (done) {
-          var lowerBound = elements[Math.floor(Math.random() * elements.length)]
-          var expectedResults = elements.filter(function (e, pos) {
-            return (Y.utils.smaller(lowerBound, e) || Y.utils.compareIds(e, lowerBound)) && elements.indexOf(e) === pos
-          }).length
-
-          var actualResults = 0
-          store.requestTransaction(function * () {
-            yield* this.os.iterate(this, lowerBound, null, function * (val) {
-              expect(val).toBeDefined()
-              actualResults++
-            })
-            expect(expectedResults).toEqual(actualResults)
-            done()
-          })
-        })
-
-        it('iterating over a tree without bounds yield the right amount of results', function (done) {
-          var lowerBound = null
-          var expectedResults = elements.filter(function (e, pos) {
-            return elements.indexOf(e) === pos
-          }).length
-          var actualResults = 0
-          store.requestTransaction(function * () {
-            yield* this.os.iterate(this, lowerBound, null, function * (val) {
-              expect(val).toBeDefined()
-              actualResults++
-            })
-            expect(expectedResults).toEqual(actualResults)
-            done()
-          })
-        })
-
-        it('iterating over a tree with upper bound yields the right amount of results', function (done) {
-          var upperBound = elements[Math.floor(Math.random() * elements.length)]
-          var expectedResults = elements.filter(function (e, pos) {
-            return (Y.utils.smaller(e, upperBound) || Y.utils.compareIds(e, upperBound)) && elements.indexOf(e) === pos
-          }).length
-
-          var actualResults = 0
-          store.requestTransaction(function * () {
-            yield* this.os.iterate(this, null, upperBound, function * (val) {
-              expect(val).toBeDefined()
-              actualResults++
-            })
-            expect(expectedResults).toEqual(actualResults)
-            done()
-          })
-        })
-
-        it('iterating over a tree with upper and lower bounds yield the right amount of results', function (done) {
-          var b1 = elements[Math.floor(Math.random() * elements.length)]
-          var b2 = elements[Math.floor(Math.random() * elements.length)]
-          var upperBound, lowerBound
-          if (Y.utils.smaller(b1, b2)) {
-            lowerBound = b1
-            upperBound = b2
-          } else {
-            lowerBound = b2
-            upperBound = b1
-          }
-          var expectedResults = elements.filter(function (e, pos) {
-            return (Y.utils.smaller(lowerBound, e) || Y.utils.compareIds(e, lowerBound)) &&
-              (Y.utils.smaller(e, upperBound) || Y.utils.compareIds(e, upperBound)) && elements.indexOf(e) === pos
-          }).length
-          var actualResults = 0
-          store.requestTransaction(function * () {
-            yield* this.os.iterate(this, lowerBound, upperBound, function * (val) {
-              expect(val).toBeDefined()
-              actualResults++
-            })
-            expect(expectedResults).toEqual(actualResults)
-            done()
-          })
-        })
-      })
-    })
-  })
-}
--- a/src/Databases/IndexedDB.js
+++ b/src/Databases/IndexedDB.js
@@ -1,181 +0,0 @@
-/* global Y */
-
-'use strict'
-
-Y.IndexedDB = (function () {
-  class Store {
-    constructor (transaction, name) {
-      this.store = transaction.objectStore(name)
-    }
-    * find (id) {
-      return yield this.store.get(id)
-    }
-    * put (v) {
-      yield this.store.put(v)
-    }
-    * delete (id) {
-      yield this.store.delete(id)
-    }
-    * findWithLowerBound (start) {
-      return yield this.store.openCursor(window.IDBKeyRange.lowerBound(start))
-    }
-    * findWithUpperBound (end) {
-      return yield this.store.openCursor(window.IDBKeyRange.upperBound(end), 'prev')
-    }
-    * findNext (id) {
-      return yield* this.findWithLowerBound([id[0], id[1] + 1])
-    }
-    * findPrev (id) {
-      return yield* this.findWithUpperBound([id[0], id[1] - 1])
-    }
-    * iterate (t, start, end, gen) {
-      var range = null
-      if (start != null && end != null) {
-        range = window.IDBKeyRange.bound(start, end)
-      } else if (start != null) {
-        range = window.IDBKeyRange.lowerBound(start)
-      } else if (end != null) {
-        range = window.IDBKeyRange.upperBound(end)
-      }
-      var cursorResult = this.store.openCursor(range)
-      while ((yield cursorResult) != null) {
-        yield* gen.call(t, cursorResult.result.value)
-        cursorResult.result.continue()
-      }
-    }
-
-  }
-  class Transaction extends Y.Transaction {
-    constructor (store) {
-      super(store)
-      var transaction = store.db.transaction(['OperationStore', 'StateStore', 'DeleteStore'], 'readwrite')
-      this.store = store
-      this.ss = new Store(transaction, 'StateStore')
-      this.os = new Store(transaction, 'OperationStore')
-      this.ds = new Store(transaction, 'DeleteStore')
-    }
-  }
-  class OperationStore extends Y.AbstractDatabase {
-    constructor (y, opts) {
-      super(y, opts)
-      if (opts == null) {
-        opts = {}
-      }
-      if (opts.namespace == null || typeof opts.namespace !== 'string') {
-        throw new Error('IndexedDB: expect a string (opts.namespace)!')
-      } else {
-        this.namespace = opts.namespace
-      }
-      if (opts.idbVersion != null) {
-        this.idbVersion = opts.idbVersion
-      } else {
-        this.idbVersion = 5
-      }
-      var store = this
-      // initialize database!
-      this.requestTransaction(function * () {
-        store.db = yield window.indexedDB.open(opts.namespace, store.idbVersion)
-      })
-      if (opts.cleanStart) {
-        this.requestTransaction(function * () {
-          yield this.os.store.clear()
-          yield this.ds.store.clear()
-          yield this.ss.store.clear()
-        })
-      }
-      var operationsToAdd = []
-      window.addEventListener('storage', function (event) {
-        if (event.key === '__YJS__' + store.namespace) {
-          operationsToAdd.push(event.newValue)
-          if (operationsToAdd.length === 1) {
-            store.requestTransaction(function * () {
-              var add = operationsToAdd
-              operationsToAdd = []
-              for (var i in add) {
-                // don't call the localStorage event twice..
-                var op = JSON.parse(add[i])
-                if (op.struct !== 'Delete') {
-                  op = yield* this.getOperation(op.id)
-                }
-                yield* this.store.operationAdded(this, op, true)
-              }
-            })
-          }
-        }
-      }, false)
-    }
-    * operationAdded (transaction, op, noAdd) {
-      yield* super.operationAdded(transaction, op)
-      if (!noAdd) {
-        window.localStorage['__YJS__' + this.namespace] = JSON.stringify(op)
-      }
-    }
-    transact (makeGen) {
-      var transaction = this.db != null ? new Transaction(this) : null
-      var store = this
-
-      var gen = makeGen.call(transaction)
-      handleTransactions(gen.next())
-
-      function handleTransactions (result) {
-        var request = result.value
-        if (result.done) {
-          makeGen = store.getNextRequest()
-          if (makeGen != null) {
-            if (transaction == null && store.db != null) {
-              transaction = new Transaction(store)
-            }
-            gen = makeGen.call(transaction)
-            handleTransactions(gen.next())
-          } // else no transaction in progress!
-          return
-        }
-        if (request.constructor === window.IDBRequest) {
-          request.onsuccess = function () {
-            var res = request.result
-            if (res != null && res.constructor === window.IDBCursorWithValue) {
-              res = res.value
-            }
-            handleTransactions(gen.next(res))
-          }
-          request.onerror = function (err) {
-            gen.throw(err)
-          }
-        } else if (request.constructor === window.IDBCursor) {
-          request.onsuccess = function () {
-            handleTransactions(gen.next(request.result != null ? request.result.value : null))
-          }
-          request.onerror = function (err) {
-            gen.throw(err)
-          }
-        } else if (request.constructor === window.IDBOpenDBRequest) {
-          request.onsuccess = function (event) {
-            var db = event.target.result
-            handleTransactions(gen.next(db))
-          }
-          request.onerror = function () {
-            gen.throw("Couldn't open IndexedDB database!")
-          }
-          request.onupgradeneeded = function (event) {
-            var db = event.target.result
-            try {
-              db.createObjectStore('OperationStore', {keyPath: 'id'})
-              db.createObjectStore('DeleteStore', {keyPath: 'id'})
-              db.createObjectStore('StateStore', {keyPath: 'id'})
-            } catch (e) {
-              console.log('Store already exists!')
-            }
-          }
-        } else {
-          gen.throw('You must not yield this type!')
-        }
-      }
-    }
-    // TODO: implement "free"..
-    * destroy () {
-      this.db.close()
-      yield window.indexedDB.deleteDatabase(this.namespace)
-    }
-  }
-  return OperationStore
-})()
--- a/src/Databases/IndexedDB.spec.js
+++ b/src/Databases/IndexedDB.spec.js
@@ -1,19 +0,0 @@
-/* global Y */
-/* eslint-env browser,jasmine */
-
-if (typeof window !== 'undefined' && false) {
-  describe('IndexedDB', function () {
-    var ob
-    beforeAll(function () {
-      ob = new Y.IndexedDB(null, {namespace: 'Test', gcTimeout: -1})
-    })
-
-    afterAll(function (done) {
-      ob.requestTransaction(function *() {
-        yield* ob.removeDatabase()
-        ob = null
-        done()
-      })
-    })
-  })
-}
--- a/src/Databases/Memory.js
+++ b/src/Databases/Memory.js
@@ -1,63 +0,0 @@
-/* global Y */
-'use strict'
-
-Y.Memory = (function () {
-  class Transaction extends Y.Transaction {
-    constructor (store) {
-      super(store)
-      this.store = store
-      this.ss = store.ss
-      this.os = store.os
-      this.ds = store.ds
-    }
-  }
-  class Database extends Y.AbstractDatabase {
-    constructor (y, opts) {
-      super(y, opts)
-      this.os = new Y.utils.RBTree()
-      this.ds = new Y.utils.RBTree()
-      this.ss = new Y.utils.RBTree()
-    }
-    logTable () {
-      var self = this
-      self.requestTransaction(function * () {
-        console.log('User: ', this.store.y.connector.userId, "==============================") // eslint-disable-line
-        console.log("State Set (SS):", yield* this.getStateSet()) // eslint-disable-line
-        console.log("Operation Store (OS):") // eslint-disable-line
-        yield* this.os.logTable() // eslint-disable-line
-        console.log("Deletion Store (DS):") //eslint-disable-line
-        yield* this.ds.logTable() // eslint-disable-line
-        if (this.store.gc1.length > 0 || this.store.gc2.length > 0) {
-          console.warn('GC1|2 not empty!', this.store.gc1, this.store.gc2)
-        }
-        if (JSON.stringify(this.store.listenersById) !== '{}') {
-          console.warn('listenersById not empty!')
-        }
-        if (JSON.stringify(this.store.listenersByIdExecuteNow) !== '[]') {
-          console.warn('listenersByIdExecuteNow not empty!')
-        }
-        if (this.store.transactionInProgress) {
-          console.warn('Transaction still in progress!')
-        }
-      }, true)
-    }
-    transact (makeGen) {
-      var t = new Transaction(this)
-      while (makeGen !== null) {
-        var gen = makeGen.call(t)
-        var res = gen.next()
-        while (!res.done) {
-          res = gen.next(res.value)
-        }
-        makeGen = this.getNextRequest()
-      }
-    }
-    * destroy () {
-      super.destroy()
-      delete this.os
-      delete this.ss
-      delete this.ds
-    }
-  }
-  return Database
-})()
--- a/src/Databases/RedBlackTree.js
+++ b/src/Databases/RedBlackTree.js
@@ -1,489 +0,0 @@
-/* global Y */
-'use strict'
-
-/*
-  This file contains a not so fancy implemantion of a Red Black Tree.
-*/
-
-class N {
-  // A created node is always red!
-  constructor (val) {
-    this.val = val
-    this.color = true
-    this._left = null
-    this._right = null
-    this._parent = null
-    if (val.id === null) {
-      throw new Error('You must define id!')
-    }
-  }
-  isRed () { return this.color }
-  isBlack () { return !this.color }
-  redden () { this.color = true; return this }
-  blacken () { this.color = false; return this }
-  get grandparent () {
-    return this.parent.parent
-  }
-  get parent () {
-    return this._parent
-  }
-  get sibling () {
-    return (this === this.parent.left)
-      ? this.parent.right : this.parent.left
-  }
-  get left () {
-    return this._left
-  }
-  get right () {
-    return this._right
-  }
-  set left (n) {
-    if (n !== null) {
-      n._parent = this
-    }
-    this._left = n
-  }
-  set right (n) {
-    if (n !== null) {
-      n._parent = this
-    }
-    this._right = n
-  }
-  rotateLeft (tree) {
-    var parent = this.parent
-    var newParent = this.right
-    var newRight = this.right.left
-    newParent.left = this
-    this.right = newRight
-    if (parent === null) {
-      tree.root = newParent
-      newParent._parent = null
-    } else if (parent.left === this) {
-      parent.left = newParent
-    } else if (parent.right === this) {
-      parent.right = newParent
-    } else {
-      throw new Error('The elements are wrongly connected!')
-    }
-  }
-  next () {
-    if (this.right !== null) {
-      // search the most left node in the right tree
-      var o = this.right
-      while (o.left !== null) {
-        o = o.left
-      }
-      return o
-    } else {
-      var p = this
-      while (p.parent !== null && p !== p.parent.left) {
-        p = p.parent
-      }
-      return p.parent
-    }
-  }
-  prev () {
-    if (this.left !== null) {
-      // search the most right node in the left tree
-      var o = this.left
-      while (o.right !== null) {
-        o = o.right
-      }
-      return o
-    } else {
-      var p = this
-      while (p.parent !== null && p !== p.parent.right) {
-        p = p.parent
-      }
-      return p.parent
-    }
-  }
-  rotateRight (tree) {
-    var parent = this.parent
-    var newParent = this.left
-    var newLeft = this.left.right
-    newParent.right = this
-    this.left = newLeft
-    if (parent === null) {
-      tree.root = newParent
-      newParent._parent = null
-    } else if (parent.left === this) {
-      parent.left = newParent
-    } else if (parent.right === this) {
-      parent.right = newParent
-    } else {
-      throw new Error('The elements are wrongly connected!')
-    }
-  }
-  getUncle () {
-    // we can assume that grandparent exists when this is called!
-    if (this.parent === this.parent.parent.left) {
-      return this.parent.parent.right
-    } else {
-      return this.parent.parent.left
-    }
-  }
-}
-
-class RBTree {
-  constructor () {
-    this.root = null
-    this.length = 0
-  }
-  * findNext (id) {
-    return yield* this.findWithLowerBound([id[0], id[1] + 1])
-  }
-  * findPrev (id) {
-    return yield* this.findWithUpperBound([id[0], id[1] - 1])
-  }
-  findNodeWithLowerBound (from) {
-    if (from === void 0) {
-      throw new Error('You must define from!')
-    }
-    var o = this.root
-    if (o === null) {
-      return null
-    } else {
-      while (true) {
-        if ((from === null || Y.utils.smaller(from, o.val.id)) && o.left !== null) {
-          // o is included in the bound
-          // try to find an element that is closer to the bound
-          o = o.left
-        } else if (from !== null && Y.utils.smaller(o.val.id, from)) {
-          // o is not within the bound, maybe one of the right elements is..
-          if (o.right !== null) {
-            o = o.right
-          } else {
-            // there is no right element. Search for the next bigger element,
-            // this should be within the bounds
-            return o.next()
-          }
-        } else {
-          return o
-        }
-      }
-    }
-  }
-  findNodeWithUpperBound (to) {
-    if (to === void 0) {
-      throw new Error('You must define from!')
-    }
-    var o = this.root
-    if (o === null) {
-      return null
-    } else {
-      while (true) {
-        if ((to === null || Y.utils.smaller(o.val.id, to)) && o.right !== null) {
-          // o is included in the bound
-          // try to find an element that is closer to the bound
-          o = o.right
-        } else if (to !== null && Y.utils.smaller(to, o.val.id)) {
-          // o is not within the bound, maybe one of the left elements is..
-          if (o.left !== null) {
-            o = o.left
-          } else {
-            // there is no left element. Search for the prev smaller element,
-            // this should be within the bounds
-            return o.prev()
-          }
-        } else {
-          return o
-        }
-      }
-    }
-  }
-  * findWithLowerBound (from) {
-    var n = this.findNodeWithLowerBound(from)
-    return n == null ? null : n.val
-  }
-  * findWithUpperBound (to) {
-    var n = this.findNodeWithUpperBound(to)
-    return n == null ? null : n.val
-  }
-  * iterate (t, from, to, f) {
-    var o = this.findNodeWithLowerBound(from)
-    while (o !== null && (to === null || Y.utils.smaller(o.val.id, to) || Y.utils.compareIds(o.val.id, to))) {
-      yield* f.call(t, o.val)
-      o = o.next()
-    }
-    return true
-  }
-  * logTable (from, to, filter) {
-    if (filter == null) {
-      filter = function () {
-        return true
-      }
-    }
-    if (from == null) { from = null }
-    if (to == null) { to = null }
-    var os = []
-    yield* this.iterate(this, from, to, function * (o) {
-      if (filter(o)) {
-        var o_ = {}
-        for (var key in o) {
-          if (typeof o[key] === 'object') {
-            o_[key] = JSON.stringify(o[key])
-          } else {
-            o_[key] = o[key]
-          }
-        }
-        os.push(o_)
-      }
-    })
-    if (console.table != null) {
-      console.table(os)
-    }
-  }
-  * find (id) {
-    var n
-    return (n = this.findNode(id)) ? n.val : null
-  }
-  findNode (id) {
-    if (id == null || id.constructor !== Array) {
-      throw new Error('Expect id to be an array!')
-    }
-    var o = this.root
-    if (o === null) {
-      return false
-    } else {
-      while (true) {
-        if (o === null) {
-          return false
-        }
-        if (Y.utils.smaller(id, o.val.id)) {
-          o = o.left
-        } else if (Y.utils.smaller(o.val.id, id)) {
-          o = o.right
-        } else {
-          return o
-        }
-      }
-    }
-  }
-  * delete (id) {
-    if (id == null || id.constructor !== Array) {
-      throw new Error('id is expected to be an Array!')
-    }
-    var d = this.findNode(id)
-    if (d == null) {
-      throw new Error('Element does not exist!')
-    }
-    this.length--
-    if (d.left !== null && d.right !== null) {
-      // switch d with the greates element in the left subtree.
-      // o should have at most one child.
-      var o = d.left
-      // find
-      while (o.right !== null) {
-        o = o.right
-      }
-      // switch
-      d.val = o.val
-      d = o
-    }
-    // d has at most one child
-    // let n be the node that replaces d
-    var isFakeChild
-    var child = d.left || d.right
-    if (child === null) {
-      isFakeChild = true
-      child = new N({id: 0})
-      child.blacken()
-      d.right = child
-    } else {
-      isFakeChild = false
-    }
-
-    if (d.parent === null) {
-      if (!isFakeChild) {
-        this.root = child
-        child.blacken()
-        child._parent = null
-      } else {
-        this.root = null
-      }
-      return
-    } else if (d.parent.left === d) {
-      d.parent.left = child
-    } else if (d.parent.right === d) {
-      d.parent.right = child
-    } else {
-      throw new Error('Impossible!')
-    }
-    if (d.isBlack()) {
-      if (child.isRed()) {
-        child.blacken()
-      } else {
-        this._fixDelete(child)
-      }
-    }
-    this.root.blacken()
-    if (isFakeChild) {
-      if (child.parent.left === child) {
-        child.parent.left = null
-      } else if (child.parent.right === child) {
-        child.parent.right = null
-      } else {
-        throw new Error('Impossible #3')
-      }
-    }
-  }
-  _fixDelete (n) {
-    function isBlack (node) {
-      return node !== null ? node.isBlack() : true
-    }
-    function isRed (node) {
-      return node !== null ? node.isRed() : false
-    }
-    if (n.parent === null) {
-      // this can only be called after the first iteration of fixDelete.
-      return
-    }
-    // d was already replaced by the child
-    // d is not the root
-    // d and child are black
-    var sibling = n.sibling
-    if (isRed(sibling)) {
-      // make sibling the grandfather
-      n.parent.redden()
-      sibling.blacken()
-      if (n === n.parent.left) {
-        n.parent.rotateLeft(this)
-      } else if (n === n.parent.right) {
-        n.parent.rotateRight(this)
-      } else {
-        throw new Error('Impossible #2')
-      }
-      sibling = n.sibling
-    }
-    // parent, sibling, and children of n are black
-    if (n.parent.isBlack() &&
-      sibling.isBlack() &&
-      isBlack(sibling.left) &&
-      isBlack(sibling.right)
-    ) {
-      sibling.redden()
-      this._fixDelete(n.parent)
-    } else if (n.parent.isRed() &&
-      sibling.isBlack() &&
-      isBlack(sibling.left) &&
-      isBlack(sibling.right)
-    ) {
-      sibling.redden()
-      n.parent.blacken()
-    } else {
-      if (n === n.parent.left &&
-        sibling.isBlack() &&
-        isRed(sibling.left) &&
-        isBlack(sibling.right)
-      ) {
-        sibling.redden()
-        sibling.left.blacken()
-        sibling.rotateRight(this)
-        sibling = n.sibling
-      } else if (n === n.parent.right &&
-        sibling.isBlack() &&
-        isRed(sibling.right) &&
-        isBlack(sibling.left)
-      ) {
-        sibling.redden()
-        sibling.right.blacken()
-        sibling.rotateLeft(this)
-        sibling = n.sibling
-      }
-      sibling.color = n.parent.color
-      n.parent.blacken()
-      if (n === n.parent.left) {
-        sibling.right.blacken()
-        n.parent.rotateLeft(this)
-      } else {
-        sibling.left.blacken()
-        n.parent.rotateRight(this)
-      }
-    }
-  }
-  * put (v) {
-    if (v == null || v.id == null || v.id.constructor !== Array) {
-      throw new Error('v is expected to have an id property which is an Array!')
-    }
-    var node = new N(v)
-    if (this.root !== null) {
-      var p = this.root // p abbrev. parent
-      while (true) {
-        if (Y.utils.smaller(node.val.id, p.val.id)) {
-          if (p.left === null) {
-            p.left = node
-            break
-          } else {
-            p = p.left
-          }
-        } else if (Y.utils.smaller(p.val.id, node.val.id)) {
-          if (p.right === null) {
-            p.right = node
-            break
-          } else {
-            p = p.right
-          }
-        } else {
-          p.val = node.val
-          return p
-        }
-      }
-      this._fixInsert(node)
-    } else {
-      this.root = node
-    }
-    this.length++
-    this.root.blacken()
-    return node
-  }
-  _fixInsert (n) {
-    if (n.parent === null) {
-      n.blacken()
-      return
-    } else if (n.parent.isBlack()) {
-      return
-    }
-    var uncle = n.getUncle()
-    if (uncle !== null && uncle.isRed()) {
-      // Note: parent: red, uncle: red
-      n.parent.blacken()
-      uncle.blacken()
-      n.grandparent.redden()
-      this._fixInsert(n.grandparent)
-    } else {
-      // Note: parent: red, uncle: black or null
-      // Now we transform the tree in such a way that
-      // either of these holds:
-      //   1) grandparent.left.isRed
-      //     and grandparent.left.left.isRed
-      //   2) grandparent.right.isRed
-      //     and grandparent.right.right.isRed
-      if (n === n.parent.right && n.parent === n.grandparent.left) {
-        n.parent.rotateLeft(this)
-        // Since we rotated and want to use the previous
-        // cases, we need to set n in such a way that
-        // n.parent.isRed again
-        n = n.left
-      } else if (n === n.parent.left && n.parent === n.grandparent.right) {
-        n.parent.rotateRight(this)
-        // see above
-        n = n.right
-      }
-      // Case 1) or 2) hold from here on.
-      // Now traverse grandparent, make parent a black node
-      // on the highest level which holds two red nodes.
-      n.parent.blacken()
-      n.grandparent.redden()
-      if (n === n.parent.left) {
-        // Case 1
-        n.grandparent.rotateRight(this)
-      } else {
-        // Case 2
-        n.grandparent.rotateLeft(this)
-      }
-    }
-  }
-}
-
-Y.utils.RBTree = RBTree
--- a/src/Databases/RedBlackTree.spec.js
+++ b/src/Databases/RedBlackTree.spec.js
@@ -1,212 +0,0 @@
-/* global Y */
-/* eslint-env browser,jasmine,console */
-
-var numberOfRBTreeTests = 1000
-
-function itRedNodesDoNotHaveBlackChildren () {
-  it('Red nodes do not have black children', function () {
-    function traverse (n) {
-      if (n == null) {
-        return
-      }
-      if (n.isRed()) {
-        if (n.left != null) {
-          expect(n.left.isRed()).not.toBeTruthy()
-        }
-        if (n.right != null) {
-          expect(n.right.isRed()).not.toBeTruthy()
-        }
-      }
-      traverse(n.left)
-      traverse(n.right)
-    }
-    traverse(this.tree.root)
-  })
-}
-
-function itBlackHeightOfSubTreesAreEqual () {
-  it('Black-height of sub-trees are equal', function () {
-    function traverse (n) {
-      if (n == null) {
-        return 0
-      }
-      var sub1 = traverse(n.left)
-      var sub2 = traverse(n.right)
-      expect(sub1).toEqual(sub2)
-      if (n.isRed()) {
-        return sub1
-      } else {
-        return sub1 + 1
-      }
-    }
-    traverse(this.tree.root)
-  })
-}
-
-function itRootNodeIsBlack () {
-  it('root node is black', function () {
-    expect(this.tree.root == null || this.tree.root.isBlack()).toBeTruthy()
-  })
-}
-
-describe('RedBlack Tree', function () {
-  var tree, memory
-  describe('debug #2', function () {
-    beforeAll(function (done) {
-      this.memory = new Y.Memory(null, {
-        name: 'Memory',
-        gcTimeout: -1
-      })
-      this.tree = this.memory.os
-      tree = this.tree
-      memory = this.memory
-      memory.requestTransaction(function * () {
-        yield* tree.put({id: [8433]})
-        yield* tree.put({id: [12844]})
-        yield* tree.put({id: [1795]})
-        yield* tree.put({id: [30302]})
-        yield* tree.put({id: [64287]})
-        yield* tree.delete([8433])
-        yield* tree.put({id: [28996]})
-        yield* tree.delete([64287])
-        yield* tree.put({id: [22721]})
-        done()
-      })
-    })
-
-    itRootNodeIsBlack()
-    itBlackHeightOfSubTreesAreEqual([])
-  })
-
-  describe(`After adding&deleting (0.8/0.2) ${numberOfRBTreeTests} times`, function () {
-    var elements = []
-    beforeAll(function (done) {
-      this.memory = new Y.Memory(null, {
-        name: 'Memory',
-        gcTimeout: -1
-      })
-      this.tree = this.memory.os
-      tree = this.tree
-      memory = this.memory
-      memory.requestTransaction(function * () {
-        for (var i = 0; i < numberOfRBTreeTests; i++) {
-          var r = Math.random()
-          if (r < 0.8) {
-            var obj = [Math.floor(Math.random() * numberOfRBTreeTests * 10000)]
-            if (!tree.findNode(obj)) {
-              elements.push(obj)
-              yield* tree.put({id: obj})
-            }
-          } else if (elements.length > 0) {
-            var elemid = Math.floor(Math.random() * elements.length)
-            var elem = elements[elemid]
-            elements = elements.filter(function (e) {
-              return !Y.utils.compareIds(e, elem)
-            })
-            yield* tree.delete(elem)
-          }
-        }
-        done()
-      })
-    })
-
-    itRootNodeIsBlack()
-
-    it('can find every object', function (done) {
-      memory.requestTransaction(function * () {
-        for (var id of elements) {
-          expect((yield* tree.find(id)).id).toEqual(id)
-        }
-        done()
-      })
-    })
-
-    it('can find every object with lower bound search', function (done) {
-      this.memory.requestTransaction(function * () {
-        for (var id of elements) {
-          expect((yield* tree.findWithLowerBound(id)).id).toEqual(id)
-        }
-        done()
-      })
-    })
-    itRedNodesDoNotHaveBlackChildren()
-
-    itBlackHeightOfSubTreesAreEqual()
-
-    it('iterating over a tree with lower bound yields the right amount of results', function (done) {
-      var lowerBound = elements[Math.floor(Math.random() * elements.length)]
-      var expectedResults = elements.filter(function (e, pos) {
-        return (Y.utils.smaller(lowerBound, e) || Y.utils.compareIds(e, lowerBound)) && elements.indexOf(e) === pos
-      }).length
-
-      var actualResults = 0
-      this.memory.requestTransaction(function * () {
-        yield* tree.iterate(this, lowerBound, null, function * (val) {
-          expect(val).toBeDefined()
-          actualResults++
-        })
-        expect(expectedResults).toEqual(actualResults)
-        done()
-      })
-    })
-
-    it('iterating over a tree without bounds yield the right amount of results', function (done) {
-      var lowerBound = null
-      var expectedResults = elements.filter(function (e, pos) {
-        return elements.indexOf(e) === pos
-      }).length
-      var actualResults = 0
-      this.memory.requestTransaction(function * () {
-        yield* tree.iterate(this, lowerBound, null, function * (val) {
-          expect(val).toBeDefined()
-          actualResults++
-        })
-        expect(expectedResults).toEqual(actualResults)
-        done()
-      })
-    })
-
-    it('iterating over a tree with upper bound yields the right amount of results', function (done) {
-      var upperBound = elements[Math.floor(Math.random() * elements.length)]
-      var expectedResults = elements.filter(function (e, pos) {
-        return (Y.utils.smaller(e, upperBound) || Y.utils.compareIds(e, upperBound)) && elements.indexOf(e) === pos
-      }).length
-
-      var actualResults = 0
-      this.memory.requestTransaction(function * () {
-        yield* tree.iterate(this, null, upperBound, function * (val) {
-          expect(val).toBeDefined()
-          actualResults++
-        })
-        expect(expectedResults).toEqual(actualResults)
-        done()
-      })
-    })
-
-    it('iterating over a tree with upper and lower bounds yield the right amount of results', function (done) {
-      var b1 = elements[Math.floor(Math.random() * elements.length)]
-      var b2 = elements[Math.floor(Math.random() * elements.length)]
-      var upperBound, lowerBound
-      if (Y.utils.smaller(b1, b2)) {
-        lowerBound = b1
-        upperBound = b2
-      } else {
-        lowerBound = b2
-        upperBound = b1
-      }
-      var expectedResults = elements.filter(function (e, pos) {
-        return (Y.utils.smaller(lowerBound, e) || Y.utils.compareIds(e, lowerBound)) &&
-          (Y.utils.smaller(e, upperBound) || Y.utils.compareIds(e, upperBound)) && elements.indexOf(e) === pos
-      }).length
-      var actualResults = 0
-      this.memory.requestTransaction(function * () {
-        yield* tree.iterate(this, lowerBound, upperBound, function * (val) {
-          expect(val).toBeDefined()
-          actualResults++
-        })
-        expect(expectedResults).toEqual(actualResults)
-        done()
-      })
-    })
-  })
-})
--- a/src/Helper.spec.js
+++ b/src/Helper.spec.js
@@ -1,288 +0,0 @@
-/* global Y */
-/* eslint-env browser, jasmine */
-
-/*
-  This is just a compilation of functions that help to test this library!
-*/
-
-// When testing, you store everything on the global object. We call it g
-var g
-if (typeof global !== 'undefined') {
-  g = global
-} else if (typeof window !== 'undefined') {
-  g = window
-} else {
-  throw new Error('No global object?')
-}
-g.g = g
-
-g.YConcurrency_TestingMode = true
-
-jasmine.DEFAULT_TIMEOUT_INTERVAL = 20000
-
-g.describeManyTimes = function describeManyTimes (times, name, f) {
-  for (var i = 0; i < times; i++) {
-    describe(name, f)
-  }
-}
-
-/*
-  Wait for a specified amount of time (in ms). defaults to 5ms
-*/
-function wait (t) {
-  if (t == null) {
-    t = 80
-  }
-  return new Promise(function (resolve) {
-    setTimeout(function () {
-      resolve()
-    }, t * 2)
-  })
-}
-g.wait = wait
-
-g.databases = ['Memory']
-if (typeof window !== 'undefined') {
-  g.databases.push('IndexedDB')
-}
-
-/*
-  returns a random element of o.
-  works on Object, and Array
-*/
-function getRandom (o) {
-  if (o instanceof Array) {
-    return o[Math.floor(Math.random() * o.length)]
-  } else if (o.constructor === Object) {
-    var ks = []
-    for (var key in o) {
-      ks.push(key)
-    }
-    return o[getRandom(ks)]
-  }
-}
-g.getRandom = getRandom
-
-function getRandomNumber (n) {
-  if (n == null) {
-    n = 9999
-  }
-  return Math.floor(Math.random() * n)
-}
-g.getRandomNumber = getRandomNumber
-
-function * applyTransactions (relAmount, numberOfTransactions, objects, users, transactions) {
-  function randomTransaction (root) {
-    var f = getRandom(transactions)
-    f(root)
-  }
-  for (var i = 0; i < numberOfTransactions * relAmount + 1; i++) {
-    var r = Math.random()
-    if (r >= 0.5) {
-      // 50% chance to flush
-      users[0].connector.flushOne() // flushes for some user.. (not necessarily 0)
-    } else if (r >= 0.05) {
-      // 45% chance to create operation
-      randomTransaction(getRandom(objects))
-    } else {
-      // 5% chance to disconnect/reconnect
-      var u = getRandom(users)
-      if (u.connector.isDisconnected()) {
-        yield u.reconnect()
-      } else {
-        yield u.disconnect()
-      }
-    }
-    yield wait()
-  }
-}
-
-g.applyRandomTransactionsAllRejoinNoGC = async(function * applyRandomTransactions (users, objects, transactions, numberOfTransactions) {
-  yield* applyTransactions(1, numberOfTransactions, objects, users, transactions)
-  yield users[0].connector.flushAll()
-  yield wait()
-  for (var u in users) {
-    yield users[u].reconnect()
-  }
-  yield wait(100)
-  yield users[0].connector.flushAll()
-  yield g.garbageCollectAllUsers(users)
-})
-
-g.applyRandomTransactionsWithGC = async(function * applyRandomTransactions (users, objects, transactions, numberOfTransactions) {
-  yield* applyTransactions(1, numberOfTransactions, objects, users.slice(1), transactions)
-  yield users[0].connector.flushAll()
-  yield g.garbageCollectAllUsers(users)
-  yield wait(100)
-  for (var u in users) {
-    // TODO: here, we enforce that two users never sync at the same time with u[0]
-    //       enforce that in the connector itself!
-    yield users[u].reconnect()
-  }
-  yield wait(100)
-  yield users[0].connector.flushAll()
-  yield wait(100)
-  yield g.garbageCollectAllUsers(users)
-})
-
-g.garbageCollectAllUsers = async(function * garbageCollectAllUsers (users) {
-  // gc two times because of the two gc phases (really collect everything)
-  yield wait(100)
-  for (var i in users) {
-    yield users[i].db.garbageCollect()
-    yield users[i].db.garbageCollect()
-  }
-  yield wait(100)
-})
-
-g.compareAllUsers = async(function * compareAllUsers (users) {
-  var s1, s2 // state sets
-  var ds1, ds2 // delete sets
-  var allDels1, allDels2 // all deletions
-  var db1 = [] // operation store of user1
-
-  // t1 and t2 basically do the same. They define t[1,2], ds[1,2], and allDels[1,2]
-  function * t1 () {
-    s1 = yield* this.getStateSet()
-    ds1 = yield* this.getDeleteSet()
-    allDels1 = []
-    yield* this.ds.iterate(this, null, null, function * (d) {
-      allDels1.push(d)
-    })
-  }
-  function * t2 () {
-    s2 = yield* this.getStateSet()
-    ds2 = yield* this.getDeleteSet()
-    allDels2 = []
-    yield* this.ds.iterate(this, null, null, function * (d) {
-      allDels2.push(d)
-    })
-  }
-  yield users[0].connector.flushAll()
-  yield wait()
-  yield g.garbageCollectAllUsers(users)
-
-  for (var uid = 0; uid < users.length; uid++) {
-    var u = users[uid]
-    u.db.requestTransaction(function * () {
-      // compare deleted ops against deleteStore
-      yield* this.os.iterate(this, null, null, function * (o) {
-        if (o.deleted === true) {
-          expect(yield* this.isDeleted(o.id)).toBeTruthy()
-        }
-      })
-      // compare deleteStore against deleted ops
-      var ds = []
-      yield* this.ds.iterate(this, null, null, function * (d) {
-        ds.push(d)
-      })
-      for (var j in ds) {
-        var d = ds[j]
-        for (var i = 0; i < d.len; i++) {
-          var o = yield* this.getOperation([d.id[0], d.id[1] + i])
-          // gc'd or deleted
-          if (d.gc) {
-            expect(o).toBeFalsy()
-          } else {
-            expect(o.deleted).toBeTruthy()
-          }
-        }
-      }
-    })
-    // compare allDels tree
-    yield wait()
-    if (s1 == null) {
-      u.db.requestTransaction(function * () {
-        yield* t1.call(this)
-        yield* this.os.iterate(this, null, null, function * (o) {
-          o = Y.utils.copyObject(o)
-          delete o.origin
-          db1.push(o)
-        })
-      })
-      yield wait()
-    } else {
-      // TODO: make requestTransaction return a promise..
-      u.db.requestTransaction(function * () {
-        yield* t2.call(this)
-        expect(s1).toEqual(s2)
-        expect(allDels1).toEqual(allDels2) // inner structure
-        expect(ds1).toEqual(ds2) // exported structure
-        var count = 0
-        yield* this.os.iterate(this, null, null, function * (o) {
-          o = Y.utils.copyObject(o)
-          delete o.origin
-          expect(db1[count++]).toEqual(o)
-        })
-      })
-      yield wait()
-    }
-  }
-})
-
-g.createUsers = async(function * createUsers (self, numberOfUsers, database) {
-  if (Y.utils.globalRoom.users[0] != null) {
-    yield Y.utils.globalRoom.users[0].flushAll()
-  }
-  // destroy old users
-  for (var u in Y.utils.globalRoom.users) {
-    Y.utils.globalRoom.users[u].y.destroy()
-  }
-  self.users = null
-
-  var promises = []
-  for (var i = 0; i < numberOfUsers; i++) {
-    promises.push(Y({
-      db: {
-        name: database,
-        namespace: 'User ' + i,
-        cleanStart: true,
-        gcTimeout: -1
-      },
-      connector: {
-        name: 'Test',
-        debug: false
-      }
-    }))
-  }
-  self.users = yield Promise.all(promises)
-  return self.users
-})
-
-/*
-  Until async/await arrives in js, we use this function to wait for promises
-  by yielding them.
-*/
-function async (makeGenerator) {
-  return function (arg) {
-    var generator = makeGenerator.apply(this, arguments)
-
-    function handle (result) {
-      if (result.done) return Promise.resolve(result.value)
-
-      return Promise.resolve(result.value).then(function (res) {
-        return handle(generator.next(res))
-      }, function (err) {
-        return handle(generator.throw(err))
-      })
-    }
-    try {
-      return handle(generator.next())
-    } catch (ex) {
-      generator.throw(ex)
-      // return Promise.reject(ex)
-    }
-  }
-}
-g.async = async
-
-function logUsers (self) {
-  if (self.constructor === Array) {
-    self = {users: self}
-  }
-  self.users[0].db.logTable()
-  self.users[1].db.logTable()
-  self.users[2].db.logTable()
-}
-
-g.logUsers = logUsers
--- a/src/Notes.md
+++ b/src/Notes.md
@@ -1,12 +0,0 @@
-
-# Notes
-
-### Terminology
-
-* DB: DataBase that holds all the information of the shared object. It is devided into the OS, DS, and SS. This can be a persistent database or an in-memory database. Depending on the type of database, it could make sense to store OS, DS, and SS in different tables, or maybe different databases.
-* OS: OperationStore holds all the operations. An operation is a js object with a fixed number of name fields.
-* DS: DeleteStore holds the information about which operations are deleted and which operations were garbage collected (no longer available in the OS).
-* SS: StateSet holds the current state of the OS. SS.getState(username) refers to the amount of operations that were received by that respective user.
-* Op: Operation defines an action on a shared type. But it is also the format in which we store the model of a type. This is why it is also called a Struct/Structure.
-* Type and Structure: We crearly distinguish between type and structure. Short explanation: A type (e.g. Strings, Numbers) have a number of functions that you can apply on them. (+) is well defined on both of them. They are *modeled* by a structure - the functions really change the structure of a type. Types can be implemented differently but still provide the same functionality. In Yjs, almost all types are realized as a doubly linked list (on which Yjs can provide eventual convergence)
-*
--- a/src/Struct.js
+++ b/src/Struct.js
@@ -1,336 +0,0 @@
-/* global Y */
-'use strict'
-
-/*
- An operation also defines the structure of a type. This is why operation and
- structure are used interchangeably here.
-
- It must be of the type Object. I hope to achieve some performance
- improvements when working on databases that support the json format.
-
- An operation must have the following properties:
-
- * encode
-     - Encode the structure in a readable format (preferably string- todo)
- * decode (todo)
-     - decode structure to json
- * execute
-     - Execute the semantics of an operation.
- * requiredOps
-     - Operations that are required to execute this operation.
-*/
-
-var Struct = {
-  /* This is the only operation that is actually not a structure, because
-  it is not stored in the OS. This is why it _does not_ have an id
-
-  op = {
-    target: Id
-  }
-  */
-  Delete: {
-    encode: function (op) {
-      return op
-    },
-    requiredOps: function (op) {
-      return [] // [op.target]
-    },
-    execute: function * (op) {
-      return yield* this.deleteOperation(op.target)
-    }
-  },
-  Insert: {
-    /* {
-        content: any,
-        id: Id,
-        left: Id,
-        origin: Id,
-        right: Id,
-        parent: Id,
-        parentSub: string (optional), // child of Map type
-      }
-    */
-    encode: function (op) {
-      // TODO: you could not send the "left" property, then you also have to
-      // "op.left = null" in $execute or $decode
-      var e = {
-        id: op.id,
-        left: op.left,
-        right: op.right,
-        origin: op.origin,
-        parent: op.parent,
-        struct: op.struct
-      }
-      if (op.parentSub != null) {
-        e.parentSub = op.parentSub
-      }
-      if (op.opContent != null) {
-        e.opContent = op.opContent
-      } else {
-        e.content = op.content
-      }
-
-      return e
-    },
-    requiredOps: function (op) {
-      var ids = []
-      if (op.left != null) {
-        ids.push(op.left)
-      }
-      if (op.right != null) {
-        ids.push(op.right)
-      }
-      if (op.origin != null && !Y.utils.compareIds(op.left, op.origin)) {
-        ids.push(op.origin)
-      }
-      // if (op.right == null && op.left == null) {
-      ids.push(op.parent)
-
-      if (op.opContent != null) {
-        ids.push(op.opContent)
-      }
-      return ids
-    },
-    getDistanceToOrigin: function * (op) {
-      if (op.left == null) {
-        return 0
-      } else {
-        var d = 0
-        var o = yield* this.getOperation(op.left)
-        while (!Y.utils.compareIds(op.origin, (o ? o.id : null))) {
-          d++
-          if (o.left == null) {
-            break
-          } else {
-            o = yield* this.getOperation(o.left)
-          }
-        }
-        return d
-      }
-    },
-    /*
-    # $this has to find a unique position between origin and the next known character
-    # case 1: $origin equals $o.origin: the $creator parameter decides if left or right
-    #         let $OL= [o1,o2,o3,o4], whereby $this is to be inserted between o1 and o4
-    #         o2,o3 and o4 origin is 1 (the position of o2)
-    #         there is the case that $this.creator < o2.creator, but o3.creator < $this.creator
-    #         then o2 knows o3. Since on another client $OL could be [o1,o3,o4] the problem is complex
-    #         therefore $this would be always to the right of o3
-    # case 2: $origin < $o.origin
-    #         if current $this insert_position > $o origin: $this ins
-    #         else $insert_position will not change
-    #         (maybe we encounter case 1 later, then this will be to the right of $o)
-    # case 3: $origin > $o.origin
-    #         $this insert_position is to the left of $o (forever!)
-    */
-    execute: function *(op) {
-      var i // loop counter
-      var distanceToOrigin = i = yield* Struct.Insert.getDistanceToOrigin.call(this, op) // most cases: 0 (starts from 0)
-      var o
-      var parent
-      var start
-
-      // find o. o is the first conflicting operation
-      if (op.left != null) {
-        o = yield* this.getOperation(op.left)
-        o = (o.right == null) ? null : yield* this.getOperation(o.right)
-      } else { // left == null
-        parent = yield* this.getOperation(op.parent)
-        let startId = op.parentSub ? parent.map[op.parentSub] : parent.start
-        start = startId == null ? null : yield* this.getOperation(startId)
-        o = start
-      }
-
-      // handle conflicts
-      while (true) {
-        if (o != null && !Y.utils.compareIds(o.id, op.right)) {
-          var oOriginDistance = yield* Struct.Insert.getDistanceToOrigin.call(this, o)
-          if (oOriginDistance === i) {
-            // case 1
-            if (o.id[0] < op.id[0]) {
-              op.left = o.id
-              distanceToOrigin = i + 1
-            }
-          } else if (oOriginDistance < i) {
-            // case 2
-            if (i - distanceToOrigin <= oOriginDistance) {
-              op.left = o.id
-              distanceToOrigin = i + 1
-            }
-          } else {
-            break
-          }
-          i++
-          o = o.right ? yield* this.getOperation(o.right) : null
-        } else {
-          break
-        }
-      }
-
-      // reconnect..
-      var left = null
-      var right = null
-      parent = parent || (yield* this.getOperation(op.parent))
-
-      // reconnect left and set right of op
-      if (op.left != null) {
-        left = yield* this.getOperation(op.left)
-        op.right = left.right
-        left.right = op.id
-
-        yield* this.setOperation(left)
-      } else {
-        op.right = op.parentSub ? parent.map[op.parentSub] || null : parent.start
-      }
-      // reconnect right
-      if (op.right != null) {
-        right = yield* this.getOperation(op.right)
-        right.left = op.id
-
-        // if right exists, and it is supposed to be gc'd. Remove it from the gc
-        if (right.gc != null) {
-          this.store.removeFromGarbageCollector(right)
-        }
-        yield* this.setOperation(right)
-      }
-
-      // update parents .map/start/end properties
-      if (op.parentSub != null) {
-        if (left == null) {
-          parent.map[op.parentSub] = op.id
-          yield* this.setOperation(parent)
-        }
-        // is a child of a map struct.
-        // Then also make sure that only the most left element is not deleted
-        if (op.right != null) {
-          yield* this.deleteOperation(op.right, true)
-        }
-        if (op.left != null) {
-          yield* this.deleteOperation(op.id, true)
-        }
-      } else {
-        if (right == null || left == null) {
-          if (right == null) {
-            parent.end = op.id
-          }
-          if (left == null) {
-            parent.start = op.id
-          }
-          yield* this.setOperation(parent)
-        }
-      }
-    }
-  },
-  List: {
-    /*
-    {
-      start: null,
-      end: null,
-      struct: "List",
-      type: "",
-      id: this.os.getNextOpId()
-    }
-    */
-    encode: function (op) {
-      return {
-        struct: 'List',
-        id: op.id,
-        type: op.type
-      }
-    },
-    requiredOps: function () {
-      /*
-      var ids = []
-      if (op.start != null) {
-        ids.push(op.start)
-      }
-      if (op.end != null){
-        ids.push(op.end)
-      }
-      return ids
-      */
-      return []
-    },
-    execute: function * (op) {
-      op.start = null
-      op.end = null
-    },
-    ref: function * (op, pos) {
-      if (op.start == null) {
-        return null
-      }
-      var res = null
-      var o = yield* this.getOperation(op.start)
-
-      while (true) {
-        if (!o.deleted) {
-          res = o
-          pos--
-        }
-        if (pos >= 0 && o.right != null) {
-          o = (yield* this.getOperation(o.right))
-        } else {
-          break
-        }
-      }
-      return res
-    },
-    map: function * (o, f) {
-      o = o.start
-      var res = []
-      while (o != null) { // TODO: change to != (at least some convention)
-        var operation = yield* this.getOperation(o)
-        if (!operation.deleted) {
-          res.push(f(operation))
-        }
-        o = operation.right
-      }
-      return res
-    }
-  },
-  Map: {
-    /*
-      {
-        map: {},
-        struct: "Map",
-        type: "",
-        id: this.os.getNextOpId()
-      }
-    */
-    encode: function (op) {
-      return {
-        struct: 'Map',
-        type: op.type,
-        id: op.id,
-        map: {} // overwrite map!!
-      }
-    },
-    requiredOps: function () {
-      return []
-    },
-    execute: function * () {},
-    /*
-      Get a property by name
-    */
-    get: function * (op, name) {
-      var oid = op.map[name]
-      if (oid != null) {
-        var res = yield* this.getOperation(oid)
-        return (res == null || res.deleted) ? void 0 : (res.opContent == null
-          ? res.content : yield* this.getType(res.opContent))
-      }
-    },
-    /*
-      Delete a property by name
-    */
-    delete: function * (op, name) {
-      var v = op.map[name] || null
-      if (v != null) {
-        yield* Struct.Delete.create.call(this, {
-          target: v
-        })
-      }
-    }
-  }
-}
-Y.Struct = Struct
--- a/src/Transaction.js
+++ b/src/Transaction.js
@@ -1,653 +0,0 @@
-/* global Y */
-'use strict'
-
-/*
-  Partial definition of a transaction
-
-  A transaction provides all the the async functionality on a database.
-
-  By convention, a transaction has the following properties:
-  * ss for StateSet
-  * os for OperationStore
-  * ds for DeleteStore
-
-  A transaction must also define the following methods:
-  * checkDeleteStoreForState(state)
-    - When increasing the state of a user, an operation with an higher id
-      may already be garbage collected, and therefore it will never be received.
-      update the state to reflect this knowledge. This won't call a method to save the state!
-  * getDeleteSet(id)
-    - Get the delete set in a readable format:
-      {
-        "userX": [
-          [5,1], // starting from position 5, one operations is deleted
-          [9,4]  // starting from position 9, four operations are deleted
-        ],
-        "userY": ...
-      }
-  * getOpsFromDeleteSet(ds) -- TODO: just call this.deleteOperation(id) here
-    - get a set of deletions that need to be applied in order to get to
-      achieve the state of the supplied ds
-  * setOperation(op)
-    - write `op` to the database.
-      Note: this is allowed to return an in-memory object.
-      E.g. the Memory adapter returns the object that it has in-memory.
-      Changing values on this object will be stored directly in the database
-      without calling this function. Therefore,
-      setOperation may have no functionality in some adapters. This also has
-      implications on the way we use operations that were served from the database.
-      We try not to call copyObject, if not necessary.
-  * addOperation(op)
-    - add an operation to the database.
-      This may only be called once for every op.id
-      Must return a function that returns the next operation in the database (ordered by id)
-  * getOperation(id)
-  * removeOperation(id)
-    - remove an operation from the database. This is called when an operation
-      is garbage collected.
-  * setState(state)
-    - `state` is of the form
-      {
-        user: "1",
-        clock: 4
-      } <- meaning that we have four operations from user "1"
-           (with these id's respectively: 0, 1, 2, and 3)
-  * getState(user)
-  * getStateVector()
-    - Get the state of the OS in the form
-    [{
-      user: "userX",
-      clock: 11
-    },
-     ..
-    ]
-  * getStateSet()
-    - Get the state of the OS in the form
-    {
-      "userX": 11,
-      "userY": 22
-    }
-   * getOperations(startSS)
-     - Get the all the operations that are necessary in order to achive the
-       stateSet of this user, starting from a stateSet supplied by another user
-   * makeOperationReady(ss, op)
-     - this is called only by `getOperations(startSS)`. It makes an operation
-       applyable on a given SS.
-*/
-class Transaction {
-  /*
-    Get a type based on the id of its model.
-    If it does not exist yes, create it.
-    TODO: delete type from store.initializedTypes[id] when corresponding id was deleted!
-  */
-  * getType (id) {
-    var sid = JSON.stringify(id)
-    var t = this.store.initializedTypes[sid]
-    if (t == null) {
-      var op = yield* this.getOperation(id)
-      if (op != null) {
-        t = yield* Y[op.type].initType.call(this, this.store, op)
-        this.store.initializedTypes[sid] = t
-      }
-    }
-    return t
-  }
-  /*
-    Apply operations that this user created (no remote ones!)
-      * does not check for Struct.*.requiredOps()
-      * also broadcasts it through the connector
-  */
-  * applyCreatedOperations (ops) {
-    var send = []
-    for (var i = 0; i < ops.length; i++) {
-      var op = ops[i]
-      yield* this.store.tryExecute.call(this, op)
-      send.push(Y.Struct[op.struct].encode(op))
-    }
-    if (!this.store.y.connector.isDisconnected()) {
-      this.store.y.connector.broadcast({
-        type: 'update',
-        ops: send
-      })
-    }
-  }
-
-  * deleteList (start) {
-    if (this.store.y.connector.isSynced) {
-      while (start != null && this.store.y.connector.isSynced) {
-        start = (yield* this.getOperation(start))
-        start.gc = true
-        yield* this.setOperation(start)
-        // TODO: will always reset the parent..
-        this.store.gc1.push(start.id)
-        start = start.right
-      }
-    } else {
-      // TODO: when not possible??? do later in (gcWhenSynced)
-    }
-  }
-
-  /*
-    Mark an operation as deleted, and add it to the GC, if possible.
-  */
-  * deleteOperation (targetId, preventCallType) {
-    var target = yield* this.getOperation(targetId)
-    var callType = false
-
-    if (target == null || !target.deleted) {
-      yield* this.markDeleted(targetId)
-    }
-
-    if (target != null && target.gc == null) {
-      if (!target.deleted) {
-        callType = true
-        // set deleted & notify type
-        target.deleted = true
-        /*
-        if (!preventCallType) {
-          var type = this.store.initializedTypes[JSON.stringify(target.parent)]
-          if (type != null) {
-            yield* type._changed(this, {
-              struct: 'Delete',
-              target: targetId
-            })
-          }
-        }
-        */
-        // delete containing lists
-        if (target.start != null) {
-          // TODO: don't do it like this .. -.-
-          yield* this.deleteList(target.start)
-          yield* this.deleteList(target.id)
-        }
-        if (target.map != null) {
-          for (var name in target.map) {
-            yield* this.deleteList(target.map[name])
-          }
-          // TODO: here to..  (see above)
-          yield* this.deleteList(target.id)
-        }
-        if (target.opContent != null) {
-          yield* this.deleteOperation(target.opContent)
-          target.opContent = null
-        }
-      }
-      var left = target.left != null ? yield* this.getOperation(target.left) : null
-
-      this.store.addToGarbageCollector(target, left)
-
-      // set here because it was deleted and/or gc'd
-      yield* this.setOperation(target)
-
-      /*
-        Check if it is possible to add right to the gc.
-        Because this delete can't be responsible for left being gc'd,
-        we don't have to add left to the gc..
-      */
-      var right = target.right != null ? yield* this.getOperation(target.right) : null
-      if (
-        right != null &&
-        this.store.addToGarbageCollector(right, target)
-      ) {
-        yield* this.setOperation(right)
-      }
-      return callType
-    }
-  }
-  /*
-    Mark an operation as deleted&gc'd
-  */
-  * markGarbageCollected (id) {
-    // this.mem.push(["gc", id]);
-    var n = yield* this.markDeleted(id)
-    if (!n.gc) {
-      if (n.id[1] < id[1]) {
-        // un-extend left
-        var newlen = n.len - (id[1] - n.id[1])
-        n.len -= newlen
-        yield* this.ds.put(n)
-        n = {id: id, len: newlen, gc: false}
-        yield* this.ds.put(n)
-      }
-      // get prev&next before adding a new operation
-      var prev = yield* this.ds.findPrev(id)
-      var next = yield* this.ds.findNext(id)
-
-      if (id[1] < n.id[1] + n.len - 1) {
-        // un-extend right
-        yield* this.ds.put({id: [id[0], id[1] + 1], len: n.len - 1, gc: false})
-        n.len = 1
-      }
-      // set gc'd
-      n.gc = true
-      // can extend left?
-      if (
-        prev != null &&
-        prev.gc &&
-        Y.utils.compareIds([prev.id[0], prev.id[1] + prev.len], n.id)
-      ) {
-        prev.len += n.len
-        yield* this.ds.delete(n.id)
-        n = prev
-        // ds.put n here?
-      }
-      // can extend right?
-      if (
-        next != null &&
-        next.gc &&
-        Y.utils.compareIds([n.id[0], n.id[1] + n.len], next.id)
-      ) {
-        n.len += next.len
-        yield* this.ds.delete(next.id)
-      }
-      yield* this.ds.put(n)
-    }
-  }
-  /*
-    Mark an operation as deleted.
-
-    returns the delete node
-  */
-  * markDeleted (id) {
-    // this.mem.push(["del", id]);
-    var n = yield* this.ds.findWithUpperBound(id)
-    if (n != null && n.id[0] === id[0]) {
-      if (n.id[1] <= id[1] && id[1] < n.id[1] + n.len) {
-        // already deleted
-        return n
-      } else if (n.id[1] + n.len === id[1] && !n.gc) {
-        // can extend existing deletion
-        n.len++
-      } else {
-        // cannot extend left
-        n = {id: id, len: 1, gc: false}
-        yield* this.ds.put(n)
-      }
-    } else {
-      // cannot extend left
-      n = {id: id, len: 1, gc: false}
-      yield* this.ds.put(n)
-    }
-    // can extend right?
-    var next = yield* this.ds.findNext(n.id)
-    if (
-      next != null &&
-      Y.utils.compareIds([n.id[0], n.id[1] + n.len], next.id) &&
-      !next.gc
-    ) {
-      n.len = n.len + next.len
-      yield* this.ds.delete(next.id)
-    }
-    yield* this.ds.put(n)
-    return n
-  }
-  /*
-    Call this method when the client is connected&synced with the
-    other clients (e.g. master). This will query the database for
-    operations that can be gc'd and add them to the garbage collector.
-  */
-  * garbageCollectAfterSync () {
-    yield* this.os.iterate(this, null, null, function * (op) {
-      if (op.deleted && op.left != null) {
-        var left = yield* this.getOperation(op.left)
-        this.store.addToGarbageCollector(op, left)
-      }
-    })
-  }
-  /*
-    Really remove an op and all its effects.
-    The complicated case here is the Insert operation:
-    * reset left
-    * reset right
-    * reset parent.start
-    * reset parent.end
-    * reset origins of all right ops
-  */
-  * garbageCollectOperation (id) {
-    this.store.addToDebug('yield* this.garbageCollectOperation(', id, ')')
-    // check to increase the state of the respective user
-    var state = yield* this.getState(id[0])
-    if (state.clock === id[1]) {
-      state.clock++
-      // also check if more expected operations were gc'd
-      yield* this.checkDeleteStoreForState(state)
-      // then set the state
-      yield* this.setState(state)
-    }
-    yield* this.markGarbageCollected(id)
-
-    // if op exists, then clean that mess up..
-    var o = yield* this.getOperation(id)
-    if (o != null) {
-      /*
-      if (!o.deleted) {
-        yield* this.deleteOperation(id)
-        o = yield* this.getOperation(id)
-      }
-      */
-
-      // remove gc'd op from the left op, if it exists
-      if (o.left != null) {
-        var left = yield* this.getOperation(o.left)
-        left.right = o.right
-        yield* this.setOperation(left)
-      }
-      // remove gc'd op from the right op, if it exists
-      // also reset origins of right ops
-      if (o.right != null) {
-        var right = yield* this.getOperation(o.right)
-        right.left = o.left
-        if (Y.utils.compareIds(right.origin, o.id)) { // rights origin is o
-          // find new origin of right ops
-          // origin is the first left deleted operation
-          var neworigin = o.left
-          while (neworigin != null) {
-            var neworigin_ = yield* this.getOperation(neworigin)
-            if (neworigin_.deleted) {
-              break
-            }
-            neworigin = neworigin_.left
-          }
-
-          // reset origin of right
-          right.origin = neworigin
-
-          // reset origin of all right ops (except first right - duh!),
-          // until you find origin pointer to the left of o
-          var i = right.right == null ? null : yield* this.getOperation(right.right)
-          var ids = [o.id, o.right]
-          while (i != null && ids.some(function (id) {
-            return Y.utils.compareIds(id, i.origin)
-          })) {
-            if (Y.utils.compareIds(i.origin, o.id)) {
-              // reset origin of i
-              i.origin = neworigin
-              yield* this.setOperation(i)
-            }
-            // get next i
-            i = i.right == null ? null : yield* this.getOperation(i.right)
-          }
-        } /* otherwise, rights origin is to the left of o,
-             then there is no right op (from o), that origins in o */
-        yield* this.setOperation(right)
-      }
-
-      if (o.parent != null) {
-        // remove gc'd op from parent, if it exists
-        var parent = yield* this.getOperation(o.parent)
-        var setParent = false // whether to save parent to the os
-        if (o.parentSub != null) {
-          if (Y.utils.compareIds(parent.map[o.parentSub], o.id)) {
-            setParent = true
-            parent.map[o.parentSub] = o.right
-          }
-        } else {
-          if (Y.utils.compareIds(parent.start, o.id)) {
-            // gc'd op is the start
-            setParent = true
-            parent.start = o.right
-          }
-          if (Y.utils.compareIds(parent.end, o.id)) {
-            // gc'd op is the end
-            setParent = true
-            parent.end = o.left
-          }
-        }
-        if (setParent) {
-          yield* this.setOperation(parent)
-        }
-      }
-      // finally remove it from the os
-      yield* this.removeOperation(o.id)
-    }
-  }
-  * checkDeleteStoreForState (state) {
-    var n = yield* this.ds.findWithUpperBound([state.user, state.clock])
-    if (n != null && n.id[0] === state.user && n.gc) {
-      state.clock = Math.max(state.clock, n.id[1] + n.len)
-    }
-  }
-  /*
-    apply a delete set in order to get
-    the state of the supplied ds
-  */
-  * applyDeleteSet (ds) {
-    var deletions = []
-    function createDeletions (user, start, len, gc) {
-      for (var c = start; c < start + len; c++) {
-        deletions.push([user, c, gc])
-      }
-    }
-
-    for (var user in ds) {
-      var dv = ds[user]
-      var pos = 0
-      var d = dv[pos]
-      yield* this.ds.iterate(this, [user, 0], [user, Number.MAX_VALUE], function * (n) {
-        // cases:
-        // 1. d deletes something to the right of n
-        //  => go to next n (break)
-        // 2. d deletes something to the left of n
-        //  => create deletions
-        //  => reset d accordingly
-        //  *)=> if d doesn't delete anything anymore, go to next d (continue)
-        // 3. not 2) and d deletes something that also n deletes
-        //  => reset d so that it doesn't contain n's deletion
-        //  *)=> if d does not delete anything anymore, go to next d (continue)
-        while (d != null) {
-          var diff = 0 // describe the diff of length in 1) and 2)
-          if (n.id[1] + n.len <= d[0]) {
-            // 1)
-            break
-          } else if (d[0] < n.id[1]) {
-            // 2)
-            // delete maximum the len of d
-            // else delete as much as possible
-            diff = Math.min(n.id[1] - d[0], d[1])
-            createDeletions(user, d[0], diff, d[2])
-          } else {
-            // 3)
-            diff = n.id[1] + n.len - d[0] // never null (see 1)
-            if (d[2] && !n.gc) {
-              // d marks as gc'd but n does not
-              // then delete either way
-              createDeletions(user, d[0], Math.min(diff, d[1]), d[2])
-            }
-          }
-          if (d[1] <= diff) {
-            // d doesn't delete anything anymore
-            d = dv[++pos]
-          } else {
-            d[0] = d[0] + diff // reset pos
-            d[1] = d[1] - diff // reset length
-          }
-        }
-      })
-      // for the rest.. just apply it
-      for (; pos < dv.length; pos++) {
-        d = dv[pos]
-        createDeletions(user, d[0], d[1], d[2])
-      }
-    }
-    for (var i in deletions) {
-      var del = deletions[i]
-      var id = [del[0], del[1]]
-      // always try to delete..
-      var addOperation = yield* this.deleteOperation(id)
-      if (addOperation) {
-        // TODO:.. really .. here? You could prevent calling all these functions in operationAdded
-        yield* this.store.operationAdded(this, {struct: 'Delete', target: id})
-      }
-      if (del[2]) {
-        // gc
-        yield* this.garbageCollectOperation(id)
-      }
-    }
-  }
-  * isGarbageCollected (id) {
-    var n = yield* this.ds.findWithUpperBound(id)
-    return n != null && n.id[0] === id[0] && id[1] < n.id[1] + n.len && n.gc
-  }
-  /*
-    A DeleteSet (ds) describes all the deleted ops in the OS
-  */
-  * getDeleteSet () {
-    var ds = {}
-    yield* this.ds.iterate(this, null, null, function * (n) {
-      var user = n.id[0]
-      var counter = n.id[1]
-      var len = n.len
-      var gc = n.gc
-      var dv = ds[user]
-      if (dv === void 0) {
-        dv = []
-        ds[user] = dv
-      }
-      dv.push([counter, len, gc])
-    })
-    return ds
-  }
-  * isDeleted (id) {
-    var n = yield* this.ds.findWithUpperBound(id)
-    return n != null && n.id[0] === id[0] && id[1] < n.id[1] + n.len
-  }
-  * setOperation (op) {
-    yield* this.os.put(op)
-    return op
-  }
-  * addOperation (op) {
-    yield* this.os.put(op)
-  }
-  * getOperation (id) {
-    return yield* this.os.find(id)
-  }
-  * removeOperation (id) {
-    yield* this.os.delete(id)
-  }
-  * setState (state) {
-    var val = {
-      id: [state.user],
-      clock: state.clock
-    }
-    // TODO: find a way to skip this step.. (after implementing some dbs..)
-    if (yield* this.ss.find([state.user])) {
-      yield* this.ss.put(val)
-    } else {
-      yield* this.ss.put(val)
-    }
-  }
-  * getState (user) {
-    var n
-    var clock = (n = yield* this.ss.find([user])) == null ? null : n.clock
-    if (clock == null) {
-      clock = 0
-    }
-    return {
-      user: user,
-      clock: clock
-    }
-  }
-  * getStateVector () {
-    var stateVector = []
-    yield* this.ss.iterate(this, null, null, function * (n) {
-      stateVector.push({
-        user: n.id[0],
-        clock: n.clock
-      })
-    })
-    return stateVector
-  }
-  * getStateSet () {
-    var ss = {}
-    yield* this.ss.iterate(this, null, null, function * (n) {
-      ss[n.id[0]] = n.clock
-    })
-    return ss
-  }
-  * getOperations (startSS) {
-    // TODO: use bounds here!
-    if (startSS == null) {
-      startSS = {}
-    }
-    var ops = []
-
-    var endSV = yield* this.getStateVector()
-    for (var endState of endSV) {
-      var user = endState.user
-      if (user === '_') {
-        continue
-      }
-      var startPos = startSS[user] || 0
-
-      yield* this.os.iterate(this, [user, startPos], [user, Number.MAX_VALUE], function * (op) {
-        ops.push(op)
-      })
-    }
-    var res = []
-    for (var op of ops) {
-      res.push(yield* this.makeOperationReady(startSS, op))
-    }
-    return res
-  }
-  /*
-    Here, we make op executable for the receiving user.
-
-    Notes:
-      startSS: denotes to the SV that the remote user sent
-      currSS:  denotes to the state vector that the user should have if he
-               applies all already sent operations (increases is each step)
-
-    We face several problems:
-    * Execute op as is won't work because ops depend on each other
-     -> find a way so that they do not anymore
-    * When changing left, must not go more to the left than the origin
-    * When changing right, you have to consider that other ops may have op
-      as their origin, this means that you must not set one of these ops
-      as the new right (interdependencies of ops)
-    * can't just go to the right until you find the first known operation,
-      With currSS
-        -> interdependency of ops is a problem
-      With startSS
-        -> leads to inconsistencies when two users join at the same time.
-           Then the position depends on the order of execution -> error!
-
-      Solution:
-      -> re-create originial situation
-        -> set op.left = op.origin (which never changes)
-        -> set op.right
-             to the first operation that is known (according to startSS)
-             or to the first operation that has an origin that is not to the
-             right of op.
-        -> Enforces unique execution order -> happy user
-
-      Improvements: TODO
-        * Could set left to origin, or the first known operation
-          (startSS or currSS.. ?)
-          -> Could be necessary when I turn GC again.
-          -> Is a bad(ish) idea because it requires more computation
-  */
-  * makeOperationReady (startSS, op) {
-    op = Y.Struct[op.struct].encode(op)
-    op = Y.utils.copyObject(op)
-    var o = op
-    var ids = [op.id]
-    // search for the new op.right
-    // it is either the first known op (according to startSS)
-    // or the o that has no origin to the right of op
-    // (this is why we use the ids array)
-    while (o.right != null) {
-      var right = yield* this.getOperation(o.right)
-      if (o.right[1] < (startSS[o.right[0]] || 0) || !ids.some(function (id) {
-        return Y.utils.compareIds(id, right.origin)
-      })) {
-        break
-      }
-      ids.push(o.right)
-      o = right
-    }
-    op.right = o.right
-    op.left = op.origin
-    return op
-  }
-}
-Y.Transaction = Transaction
--- a/src/Types/Array.js
+++ b/src/Types/Array.js
@@ -1,192 +0,0 @@
-/* global Y */
-'use strict'
-
-;(function () {
-  class YArray {
-    constructor (os, _model, idArray, valArray) {
-      this.os = os
-      this._model = _model
-      // Array of all the operation id's
-      this.idArray = idArray
-      // Array of all the values
-      this.valArray = valArray
-      this.eventHandler = new Y.utils.EventHandler(ops => {
-        var userEvents = []
-        for (var i in ops) {
-          var op = ops[i]
-          if (op.struct === 'Insert') {
-            let pos
-            // we check op.left only!,
-            // because op.right might not be defined when this is called
-            if (op.left === null) {
-              pos = 0
-            } else {
-              var sid = JSON.stringify(op.left)
-              pos = this.idArray.indexOf(sid) + 1
-              if (pos <= 0) {
-                throw new Error('Unexpected operation!')
-              }
-            }
-            this.idArray.splice(pos, 0, JSON.stringify(op.id))
-            this.valArray.splice(pos, 0, op.content)
-            userEvents.push({
-              type: 'insert',
-              object: this,
-              index: pos,
-              length: 1
-            })
-          } else if (op.struct === 'Delete') {
-            let pos = this.idArray.indexOf(JSON.stringify(op.target))
-            if (pos >= 0) {
-              this.idArray.splice(pos, 1)
-              this.valArray.splice(pos, 1)
-              userEvents.push({
-                type: 'delete',
-                object: this,
-                index: pos,
-                length: 1
-              })
-            }
-          } else {
-            throw new Error('Unexpected struct!')
-          }
-        }
-        this.eventHandler.callEventListeners(userEvents)
-      })
-    }
-    get length () {
-      return this.idArray.length
-    }
-    get (pos) {
-      if (pos == null || typeof pos !== 'number') {
-        throw new Error('pos must be a number!')
-      }
-      return this.valArray[pos]
-    }
-    toArray () {
-      return this.valArray.slice()
-    }
-    insert (pos, contents) {
-      if (typeof pos !== 'number') {
-        throw new Error('pos must be a number!')
-      }
-      if (!(contents instanceof Array)) {
-        throw new Error('contents must be an Array of objects!')
-      }
-      if (contents.length === 0) {
-        return
-      }
-      if (pos > this.idArray.length || pos < 0) {
-        throw new Error('This position exceeds the range of the array!')
-      }
-      var mostLeft = pos === 0 ? null : JSON.parse(this.idArray[pos - 1])
-
-      var ops = []
-      var prevId = mostLeft
-      for (var i = 0; i < contents.length; i++) {
-        var op = {
-          left: prevId,
-          origin: prevId,
-          // right: mostRight,
-          // NOTE: I intentionally do not define right here, because it could be deleted
-          // at the time of creating this operation, and is therefore not defined in idArray
-          parent: this._model,
-          content: contents[i],
-          struct: 'Insert',
-          id: this.os.getNextOpId()
-        }
-        ops.push(op)
-        prevId = op.id
-      }
-      var eventHandler = this.eventHandler
-      eventHandler.awaitAndPrematurelyCall(ops)
-      this.os.requestTransaction(function *() {
-        // now we can set the right reference.
-        var mostRight
-        if (mostLeft != null) {
-          mostRight = (yield* this.getOperation(mostLeft)).right
-        } else {
-          mostRight = (yield* this.getOperation(ops[0].parent)).start
-        }
-        for (var j in ops) {
-          ops[j].right = mostRight
-        }
-        yield* this.applyCreatedOperations(ops)
-        eventHandler.awaitedInserts(ops.length)
-      })
-    }
-    delete (pos, length) {
-      if (length == null) { length = 1 }
-      if (typeof length !== 'number') {
-        throw new Error('pos must be a number!')
-      }
-      if (typeof pos !== 'number') {
-        throw new Error('pos must be a number!')
-      }
-      if (pos + length > this.idArray.length || pos < 0 || length < 0) {
-        throw new Error('The deletion range exceeds the range of the array!')
-      }
-      if (length === 0) {
-        return
-      }
-      var eventHandler = this.eventHandler
-      var newLeft = pos > 0 ? JSON.parse(this.idArray[pos - 1]) : null
-      var dels = []
-      for (var i = 0; i < length; i++) {
-        dels.push({
-          target: JSON.parse(this.idArray[pos + i]),
-          struct: 'Delete'
-        })
-      }
-      eventHandler.awaitAndPrematurelyCall(dels)
-      this.os.requestTransaction(function *() {
-        yield* this.applyCreatedOperations(dels)
-        eventHandler.awaitedDeletes(dels.length, newLeft)
-      })
-    }
-    observe (f) {
-      this.eventHandler.addEventListener(f)
-    }
-    * _changed (transaction, op) {
-      if (!op.deleted) {
-        if (op.struct === 'Insert') {
-          var l = op.left
-          var left
-          while (l != null) {
-            left = yield* transaction.getOperation(l)
-            if (!left.deleted) {
-              break
-            }
-            l = left.left
-          }
-          op.left = l
-        }
-        this.eventHandler.receivedOp(op)
-      }
-    }
-  }
-
-  Y.Array = new Y.utils.CustomType({
-    class: YArray,
-    createType: function * YArrayCreator () {
-      var modelid = this.store.getNextOpId()
-      var model = {
-        struct: 'List',
-        type: 'Array',
-        start: null,
-        end: null,
-        id: modelid
-      }
-      yield* this.applyCreatedOperations([model])
-      return modelid
-    },
-    initType: function * YArrayInitializer (os, model) {
-      var valArray = []
-      var idArray = yield* Y.Struct.List.map.call(this, model, function (c) {
-        valArray.push(c.content)
-        return JSON.stringify(c.id)
-      })
-      return new YArray(os, model.id, idArray, valArray)
-    }
-  })
-})()
--- a/src/Types/Array.spec.js
+++ b/src/Types/Array.spec.js
@@ -1,310 +0,0 @@
-/* global createUsers, databases, wait, Y, compareAllUsers, getRandomNumber, applyRandomTransactionsAllRejoinNoGC, applyRandomTransactionsWithGC, async, garbageCollectAllUsers, describeManyTimes */
-/* eslint-env browser,jasmine */
-
-var numberOfYArrayTests = 50
-var repeatArrayTests = 2
-
-for (let database of databases) {
-  describe(`Array Type (DB: ${database})`, function () {
-    var y1, y2, y3, yconfig1, yconfig2, yconfig3, flushAll
-
-    beforeEach(async(function * (done) {
-      yield createUsers(this, 3, database)
-      y1 = (yconfig1 = this.users[0]).root
-      y2 = (yconfig2 = this.users[1]).root
-      y3 = (yconfig3 = this.users[2]).root
-      flushAll = this.users[0].connector.flushAll
-      yield wait(10)
-      done()
-    }))
-    afterEach(async(function * (done) {
-      yield compareAllUsers(this.users)
-      done()
-    }))
-
-    describe('Basic tests', function () {
-      it('insert three elements, try re-get property', async(function * (done) {
-        var array = yield y1.set('Array', Y.Array)
-        array.insert(0, [1, 2, 3])
-        array = yield y1.get('Array') // re-get property
-        expect(array.toArray()).toEqual([1, 2, 3])
-        done()
-      }))
-      it('Basic insert in array (handle three conflicts)', async(function * (done) {
-        yield y1.set('Array', Y.Array)
-        yield flushAll()
-        var l1 = yield y1.get('Array')
-        l1.insert(0, [0])
-        var l2 = yield y2.get('Array')
-        l2.insert(0, [1])
-        var l3 = yield y3.get('Array')
-        l3.insert(0, [2])
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        done()
-      }))
-      it('Basic insert&delete in array (handle three conflicts)', async(function * (done) {
-        var l1, l2, l3
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y', 'z'])
-        yield flushAll()
-        l1.insert(1, [0])
-        l2 = yield y2.get('Array')
-        l2.delete(0)
-        l2.delete(1)
-        l3 = yield y3.get('Array')
-        l3.insert(1, [2])
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        expect(l2.toArray()).toEqual([0, 2, 'y'])
-        done()
-      }))
-      it('Handles getOperations ascending ids bug in late sync', async(function * (done) {
-        var l1, l2
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y'])
-        yield flushAll()
-        yconfig3.disconnect()
-        yconfig2.disconnect()
-        yield wait()
-        l2 = yield y2.get('Array')
-        l2.insert(1, [2])
-        l2.insert(1, [3])
-        yield yconfig2.reconnect()
-        yield yconfig3.reconnect()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        done()
-      }))
-      it('Handles deletions in late sync', async(function * (done) {
-        var l1, l2
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y'])
-        yield flushAll()
-        yield yconfig2.disconnect()
-        yield wait()
-        l2 = yield y2.get('Array')
-        l2.delete(1, 1)
-        l1.delete(0, 2)
-        yield yconfig2.reconnect()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        done()
-      }))
-      it('Handles deletions in late sync (2)', async(function * (done) {
-        var l1, l2
-        l1 = yield y1.set('Array', Y.Array)
-        yield flushAll()
-        l2 = yield y2.get('Array')
-        l1.insert(0, ['x', 'y'])
-        l1.delete(0, 2)
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        done()
-      }))
-      it('Basic insert. Then delete the whole array', async(function * (done) {
-        var l1, l2, l3
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y', 'z'])
-        yield flushAll()
-        l1.delete(0, 3)
-        l2 = yield y2.get('Array')
-        l3 = yield y3.get('Array')
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        expect(l2.toArray()).toEqual([])
-        done()
-      }))
-      it('Basic insert. Then delete the whole array (merge listeners on late sync)', async(function * (done) {
-        var l1, l2, l3
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y', 'z'])
-        yield flushAll()
-        yconfig2.disconnect()
-        l1.delete(0, 3)
-        l2 = yield y2.get('Array')
-        yield wait()
-        yield yconfig2.reconnect()
-        yield wait()
-        l3 = yield y3.get('Array')
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        expect(l2.toArray()).toEqual([])
-        done()
-      }))
-      // TODO?
-      /* it('Basic insert. Then delete the whole array (merge deleter on late sync)', async(function * (done) {
-        var l1, l2, l3
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y', 'z'])
-        yield flushAll()
-        yconfig1.disconnect()
-        l1.delete(0, 3)
-        l2 = yield y2.get('Array')
-        yield yconfig1.reconnect()
-        l3 = yield y3.get('Array')
-        yield flushAll()
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        expect(l2.toArray()).toEqual([])
-        done()
-      })) */
-      it('throw insert & delete events', async(function * (done) {
-        var array = yield this.users[0].root.set('array', Y.Array)
-        var event
-        array.observe(function (e) {
-          event = e
-        })
-        array.insert(0, [0])
-        expect(event).toEqual([{
-          type: 'insert',
-          object: array,
-          index: 0,
-          length: 1
-        }])
-        array.delete(0)
-        expect(event).toEqual([{
-          type: 'delete',
-          object: array,
-          index: 0,
-          length: 1
-        }])
-        yield wait(50)
-        done()
-      }))
-      it('garbage collects', async(function * (done) {
-        var l1, l2, l3
-        l1 = yield y1.set('Array', Y.Array)
-        l1.insert(0, ['x', 'y', 'z'])
-        yield flushAll()
-        yconfig1.disconnect()
-        l1.delete(0, 3)
-        l2 = yield y2.get('Array')
-        yield wait()
-        yield yconfig1.reconnect()
-        yield wait()
-        l3 = yield y3.get('Array')
-        yield flushAll()
-        yield garbageCollectAllUsers(this.users)
-        expect(l1.toArray()).toEqual(l2.toArray())
-        expect(l2.toArray()).toEqual(l3.toArray())
-        expect(l2.toArray()).toEqual([])
-        done()
-      }))
-      it('debug right not existend in Insert.execute', async(function * (done) {
-        yconfig1.db.requestTransaction(function * () {
-          var ops = [{'struct':'Map','type':'Map','id':['130',0],'map':{}},{'id':['130',1],'left':null,'right':null,'origin':null,'parent':['_',0],'struct':'Insert','parentSub':'Map','opContent':['130',0]},{'struct':'Map','type':'Map','id':['130',0],'map':{}},{'id':['130',1],'left':null,'right':null,'origin':null,'parent':['_',0],'struct':'Insert','parentSub':'Map','opContent':['130',0]},{'struct':'Map','type':'Map','id':['130',0],'map':{}},{'id':['130',1],'left':null,'right':null,'origin':null,'parent':['_',0],'struct':'Insert','parentSub':'Map','opContent':['130',0]},{'left':null,'right':null,'origin':null,'parent':['130',0],'parentSub':'somekey','struct':'Insert','content':512,'id':['133',0]},{'id':['130',2],'left':null,'right':null,'origin':null,'parent':['130',0],'struct':'Insert','parentSub':'somekey','content':1131},{'id':['130',3],'left':null,'right':['130',2],'origin':null,'parent':['130',0],'struct':'Insert','parentSub':'somekey','content':4196},{'id':['131',3],'left':null,'right':null,'origin':null,'parent':['130',0],'struct':'Insert','parentSub':'somekey','content':5022}]//eslint-disable-line
-
-          for (var o of ops) {
-            yield* this.store.tryExecute.call(this, o)
-          }
-        })
-        yield wait()
-        yield yconfig3.disconnect()
-        yield yconfig2.disconnect()
-        yield flushAll()
-        wait()
-        yield yconfig3.reconnect()
-        yield yconfig2.reconnect()
-        yield wait()
-        yield flushAll()
-        done()
-      }))
-      it('debug right not existend in Insert.execute (2)', async(function * (done) {
-        yconfig1.db.requestTransaction(function * () {
-          yield* this.store.tryExecute.call(this, {'struct': 'Map', 'type': 'Map', 'id': ['153', 0], 'map': {}})
-          yield* this.store.tryExecute.call(this, {'id': ['153', 1], 'left': null, 'right': null, 'origin': null, 'parent': ['_', 0], 'struct': 'Insert', 'parentSub': 'Map', 'opContent': ['153', 0]})
-          yield* this.store.tryExecute.call(this, {'struct': 'Map', 'type': 'Map', 'id': ['153', 0], 'map': {}})
-          yield* this.store.tryExecute.call(this, {'id': ['153', 1], 'left': null, 'right': null, 'origin': null, 'parent': ['_', 0], 'struct': 'Insert', 'parentSub': 'Map', 'opContent': ['153', 0]})
-          yield* this.store.tryExecute.call(this, {'struct': 'Map', 'type': 'Map', 'id': ['153', 0], 'map': {}})
-          yield* this.store.tryExecute.call(this, {'id': ['153', 1], 'left': null, 'right': null, 'origin': null, 'parent': ['_', 0], 'struct': 'Insert', 'parentSub': 'Map', 'opContent': ['153', 0]})
-          yield* this.store.tryExecute.call(this, {'left': null, 'right': null, 'origin': null, 'parent': ['153', 0], 'parentSub': 'somekey', 'struct': 'Insert', 'content': 3784, 'id': ['154', 0]})
-          yield* this.store.tryExecute.call(this, {'left': null, 'right': ['154', 0], 'origin': null, 'parent': ['153', 0], 'parentSub': 'somekey', 'struct': 'Insert', 'content': 8217, 'id': ['154', 1]})
-          yield* this.store.tryExecute.call(this, {'left': null, 'right': ['154', 1], 'origin': null, 'parent': ['153', 0], 'parentSub': 'somekey', 'struct': 'Insert', 'content': 5036, 'id': ['154', 2]})
-          yield* this.store.tryExecute.call(this, {'id': ['153', 2], 'left': null, 'right': null, 'origin': null, 'parent': ['153', 0], 'struct': 'Insert', 'parentSub': 'somekey', 'content': 417})
-          yield* this.store.tryExecute.call(this, {'id': ['155', 0], 'left': null, 'right': null, 'origin': null, 'parent': ['153', 0], 'struct': 'Insert', 'parentSub': 'somekey', 'content': 2202})
-          yield* this.garbageCollectOperation(['153', 2])
-          yield* this.garbageCollectOperation(['154', 0])
-          yield* this.garbageCollectOperation(['154', 1])
-          yield* this.garbageCollectOperation(['154', 2])
-          yield* this.garbageCollectOperation(['155', 0])
-          yield* this.garbageCollectOperation(['156', 0])
-          yield* this.garbageCollectOperation(['157', 0])
-          yield* this.garbageCollectOperation(['157', 1])
-          yield* this.store.tryExecute.call(this, {'id': ['153', 3], 'left': null, 'right': null, 'origin': null, 'parent': ['153', 0], 'struct': 'Insert', 'parentSub': 'somekey', 'content': 4372})
-        })
-        yield wait()
-        yield yconfig3.disconnect()
-        yield yconfig2.disconnect()
-        yield flushAll()
-        wait()
-        yield yconfig3.reconnect()
-        yield yconfig2.reconnect()
-        yield wait()
-        yield flushAll()
-        done()
-      }))
-    })
-    describeManyTimes(repeatArrayTests, `Random tests`, function () {
-      var randomArrayTransactions = [
-        function insert (array) {
-          array.insert(getRandomNumber(array.toArray().length), [getRandomNumber()])
-        },
-        function _delete (array) {
-          var length = array.toArray().length
-          if (length > 0) {
-            array.delete(getRandomNumber(length - 1))
-          }
-        }
-      ]
-      function compareArrayValues (arrays) {
-        var firstArray
-        for (var l of arrays) {
-          var val = l.toArray()
-          if (firstArray == null) {
-            firstArray = val
-          } else {
-            expect(val).toEqual(firstArray)
-          }
-        }
-      }
-      beforeEach(async(function * (done) {
-        yield this.users[0].root.set('Array', Y.Array)
-        yield flushAll()
-
-        var promises = []
-        for (var u = 0; u < this.users.length; u++) {
-          promises.push(this.users[u].root.get('Array'))
-        }
-        this.arrays = yield Promise.all(promises)
-        done()
-      }))
-      it('arrays.length equals users.length', async(function * (done) {
-        expect(this.arrays.length).toEqual(this.users.length)
-        done()
-      }))
-      it(`succeed after ${numberOfYArrayTests} actions, no GC, all users disconnecting/reconnecting`, async(function * (done) {
-        for (var u of this.users) {
-          u.connector.debug = true
-        }
-        yield applyRandomTransactionsAllRejoinNoGC(this.users, this.arrays, randomArrayTransactions, numberOfYArrayTests)
-        yield flushAll()
-        yield compareArrayValues(this.arrays)
-        yield compareAllUsers(this.users)
-        done()
-      }))
-      it(`succeed after ${numberOfYArrayTests} actions, GC, user[0] is not disconnecting`, async(function * (done) {
-        for (var u of this.users) {
-          u.connector.debug = true
-        }
-        yield applyRandomTransactionsWithGC(this.users, this.arrays, randomArrayTransactions, numberOfYArrayTests)
-        yield flushAll()
-        yield compareArrayValues(this.arrays)
-        yield compareAllUsers(this.users)
-        done()
-      }))
-    })
-  })
-}
--- a/src/Types/Map.js
+++ b/src/Types/Map.js
@@ -1,295 +0,0 @@
-/* global Y */
-'use strict'
-
-;(function () {
-  class YMap {
-    constructor (os, model, contents, opContents) {
-      this._model = model.id
-      this.os = os
-      this.map = Y.utils.copyObject(model.map)
-      this.contents = contents
-      this.opContents = opContents
-      this.eventHandler = new Y.utils.EventHandler(ops => {
-        var userEvents = []
-        for (var i in ops) {
-          var op = ops[i]
-          var oldValue
-          // key is the name to use to access (op)content
-          var key = op.struct === 'Delete' ? op.key : op.parentSub
-
-          // compute oldValue
-          if (this.opContents[key] != null) {
-            let prevType = this.opContents[key]
-            oldValue = () => {// eslint-disable-line
-              return new Promise((resolve) => {
-                this.os.requestTransaction(function *() {// eslint-disable-line
-                  resolve(yield* this.getType(prevType))
-                })
-              })
-            }
-          } else {
-            oldValue = this.contents[key]
-          }
-          // compute op event
-          if (op.struct === 'Insert') {
-            if (op.left === null) {
-              if (op.opContent != null) {
-                delete this.contents[key]
-                if (op.deleted) {
-                  delete this.opContents[key]
-                } else {
-                  this.opContents[key] = op.opContent
-                }
-              } else {
-                delete this.opContents[key]
-                if (op.deleted) {
-                  delete this.contents[key]
-                } else {
-                  this.contents[key] = op.content
-                }
-              }
-              this.map[key] = op.id
-              var insertEvent = {
-                name: key,
-                object: this
-              }
-              if (oldValue === undefined) {
-                insertEvent.type = 'add'
-              } else {
-                insertEvent.type = 'update'
-                insertEvent.oldValue = oldValue
-              }
-              userEvents.push(insertEvent)
-            }
-          } else if (op.struct === 'Delete') {
-            if (Y.utils.compareIds(this.map[key], op.target)) {
-              delete this.opContents[key]
-              delete this.contents[key]
-              var deleteEvent = {
-                name: key,
-                object: this,
-                oldValue: oldValue,
-                type: 'delete'
-              }
-              userEvents.push(deleteEvent)
-            }
-          } else {
-            throw new Error('Unexpected Operation!')
-          }
-        }
-        this.eventHandler.callEventListeners(userEvents)
-      })
-    }
-    get (key) {
-      // return property.
-      // if property does not exist, return null
-      // if property is a type, return a promise
-      if (key == null) {
-        throw new Error('You must specify key!')
-      }
-      if (this.opContents[key] == null) {
-        return this.contents[key]
-      } else {
-        return new Promise((resolve) => {
-          var oid = this.opContents[key]
-          this.os.requestTransaction(function *() {
-            resolve(yield* this.getType(oid))
-          })
-        })
-      }
-    }
-    /*
-      If there is a primitive (not a custom type), then return it.
-      Returns all primitive values, if propertyName is specified!
-      Note: modifying the return value could result in inconsistencies!
-        -- so make sure to copy it first!
-    */
-    getPrimitive (key) {
-      if (key == null) {
-        return Y.utils.copyObject(this.contents)
-      } else {
-        return this.contents[key]
-      }
-    }
-    delete (key) {
-      var right = this.map[key]
-      if (right != null) {
-        var del = {
-          target: right,
-          struct: 'Delete'
-        }
-        var eventHandler = this.eventHandler
-        var modDel = Y.utils.copyObject(del)
-        modDel.key = key
-        eventHandler.awaitAndPrematurelyCall([modDel])
-        this.os.requestTransaction(function *() {
-          yield* this.applyCreatedOperations([del])
-          eventHandler.awaitedDeletes(1)
-        })
-      }
-    }
-    set (key, value) {
-      // set property.
-      // if property is a type, return a promise
-      // if not, apply immediately on this type an call event
-
-      var right = this.map[key] || null
-      var insert = {
-        left: null,
-        right: right,
-        origin: null,
-        parent: this._model,
-        parentSub: key,
-        struct: 'Insert'
-      }
-      return new Promise((resolve) => {
-        if (value instanceof Y.utils.CustomType) {
-          // construct a new type
-          this.os.requestTransaction(function *() {
-            var typeid = yield* value.createType.call(this)
-            var type = yield* this.getType(typeid)
-            insert.opContent = typeid
-            insert.id = this.store.getNextOpId()
-            yield* this.applyCreatedOperations([insert])
-            resolve(type)
-          })
-        } else {
-          insert.content = value
-          insert.id = this.os.getNextOpId()
-          var eventHandler = this.eventHandler
-          eventHandler.awaitAndPrematurelyCall([insert])
-
-          this.os.requestTransaction(function *() {
-            yield* this.applyCreatedOperations([insert])
-            eventHandler.awaitedInserts(1)
-          })
-          resolve(value)
-        }
-      })
-    }
-    observe (f) {
-      this.eventHandler.addEventListener(f)
-    }
-    unobserve (f) {
-      this.eventHandler.removeEventListener(f)
-    }
-    /*
-      Observe a path.
-
-      E.g.
-      ```
-      o.set('textarea', Y.TextBind)
-      o.observePath(['textarea'], function(t){
-        // is called whenever textarea is replaced
-        t.bind(textarea)
-      })
-
-      returns a Promise that contains a function that removes the observer from the path.
-    */
-    observePath (path, f) {
-      var self = this
-      function observeProperty (events) {
-        // call f whenever path changes
-        for (var i = 0; i < events.length; i++) {
-          var event = events[i]
-          if (event.name === propertyName) {
-            // call this also for delete events!
-            var property = self.get(propertyName)
-            if (property instanceof Promise) {
-              property.then(f)
-            } else {
-              f(property)
-            }
-          }
-        }
-      }
-
-      if (path.length < 1) {
-        throw new Error('Path must contain at least one element!')
-      } else if (path.length === 1) {
-        var propertyName = path[0]
-        var property = self.get(propertyName)
-        if (property instanceof Promise) {
-          property.then(f)
-        } else {
-          f(property)
-        }
-        this.observe(observeProperty)
-        return Promise.resolve(function () {
-          self.unobserve(f)
-        })
-      } else {
-        var deleteChildObservers
-        var resetObserverPath = function () {
-          var promise = self.get(path[0])
-          if (!promise instanceof Promise) {
-            // its either not defined or a primitive value
-            promise = self.set(path[0], Y.Map)
-          }
-          return promise.then(function (map) {
-            return map.observePath(path.slice(1), f)
-          }).then(function (_deleteChildObservers) {
-            // update deleteChildObservers
-            deleteChildObservers = _deleteChildObservers
-            return Promise.resolve() // Promise does not return anything
-          })
-        }
-        var observer = function (events) {
-          for (var e in events) {
-            var event = events[e]
-            if (event.name === path[0]) {
-              deleteChildObservers()
-              if (event.type === 'add' || event.type === 'update') {
-                resetObserverPath()
-              }
-              // TODO: what about the delete events?
-            }
-          }
-        }
-        self.observe(observer)
-        return resetObserverPath().then(
-          // this promise contains a function that deletes all the child observers
-          // and how to unobserve the observe from this object
-          Promise.resolve(function () {
-            deleteChildObservers()
-            self.unobserve(observer)
-          })
-        )
-      }
-    }
-    * _changed (transaction, op) {
-      if (op.struct === 'Delete') {
-        op.key = (yield* transaction.getOperation(op.target)).parentSub
-      }
-      this.eventHandler.receivedOp(op)
-    }
-  }
-  Y.Map = new Y.utils.CustomType({
-    class: YMap,
-    createType: function * YMapCreator () {
-      var modelid = this.store.getNextOpId()
-      var model = {
-        map: {},
-        struct: 'Map',
-        type: 'Map',
-        id: modelid
-      }
-      yield* this.applyCreatedOperations([model])
-      return modelid
-    },
-    initType: function * YMapInitializer (os, model) {
-      var contents = {}
-      var opContents = {}
-      var map = model.map
-      for (var name in map) {
-        var op = yield* this.getOperation(map[name])
-        if (op.opContent != null) {
-          opContents[name] = op.opContent
-        } else {
-          contents[name] = op.content
-        }
-      }
-      return new YMap(os, model, contents, opContents)
-    }
-  })
-})()
--- a/src/Types/Map.spec.js
+++ b/src/Types/Map.spec.js
@@ -1,219 +0,0 @@
-/* global createUsers, Y, databases, compareAllUsers, getRandomNumber, applyRandomTransactionsAllRejoinNoGC, applyRandomTransactionsWithGC, async, describeManyTimes */
-/* eslint-env browser,jasmine */
-
-var numberOfYMapTests = 40
-var repeatMapTeasts = 2
-
-for (let database of databases) {
-  describe(`Map Type (DB: ${database})`, function () {
-    var y1, y2, y3, y4, flushAll
-
-    beforeEach(async(function * (done) {
-      yield createUsers(this, 5, database)
-      y1 = this.users[0].root
-      y2 = this.users[1].root
-      y3 = this.users[2].root
-      y4 = this.users[3].root
-      flushAll = this.users[0].connector.flushAll
-      done()
-    }))
-    afterEach(async(function * (done) {
-      yield compareAllUsers(this.users)
-      done()
-    }), 5000)
-
-    describe('Basic tests', function () {
-      it('Basic get&set of Map property (converge via sync)', async(function * (done) {
-        y1.set('stuff', 'stuffy')
-        expect(y1.get('stuff')).toEqual('stuffy')
-        yield flushAll()
-        for (var key in this.users) {
-          var u = this.users[key].root
-          expect(u.get('stuff')).toEqual('stuffy')
-        }
-        done()
-      }))
-      it('Map can set custom types (Map)', async(function * (done) {
-        var map = yield y1.set('Map', Y.Map)
-        map.set('one', 1)
-        map = yield y1.get('Map')
-        expect(map.get('one')).toEqual(1)
-        done()
-      }))
-      it('Map can set custom types (Array)', async(function * (done) {
-        var array = yield y1.set('Array', Y.Array)
-        array.insert(0, [1, 2, 3])
-        array = yield y1.get('Array')
-        expect(array.toArray()).toEqual([1, 2, 3])
-        done()
-      }))
-      it('Basic get&set of Map property (converge via update)', async(function * (done) {
-        yield flushAll()
-        y1.set('stuff', 'stuffy')
-        expect(y1.get('stuff')).toEqual('stuffy')
-
-        yield flushAll()
-        for (var key in this.users) {
-          var r = this.users[key].root
-          expect(r.get('stuff')).toEqual('stuffy')
-        }
-        done()
-      }))
-      it('Basic get&set of Map property (handle conflict)', async(function * (done) {
-        yield flushAll()
-        y1.set('stuff', 'c0')
-        y2.set('stuff', 'c1')
-
-        yield flushAll()
-        for (var key in this.users) {
-          var u = this.users[key]
-          expect(u.root.get('stuff')).toEqual('c0')
-        }
-        done()
-      }))
-      it('Basic get&set&delete of Map property (handle conflict)', async(function * (done) {
-        yield flushAll()
-        y1.set('stuff', 'c0')
-        y1.delete('stuff')
-        y2.set('stuff', 'c1')
-        yield flushAll()
-
-        for (var key in this.users) {
-          var u = this.users[key]
-          expect(u.root.get('stuff')).toBeUndefined()
-        }
-        done()
-      }))
-      it('Basic get&set of Map property (handle three conflicts)', async(function * (done) {
-        yield flushAll()
-        y1.set('stuff', 'c0')
-        y2.set('stuff', 'c1')
-        y2.set('stuff', 'c2')
-        y3.set('stuff', 'c3')
-        yield flushAll()
-
-        for (var key in this.users) {
-          var u = this.users[key]
-          expect(u.root.get('stuff')).toEqual('c0')
-        }
-        done()
-      }))
-      it('Basic get&set&delete of Map property (handle three conflicts)', async(function * (done) {
-        yield flushAll()
-        y1.set('stuff', 'c0')
-        y2.set('stuff', 'c1')
-        y2.set('stuff', 'c2')
-        y3.set('stuff', 'c3')
-        yield flushAll()
-        y1.set('stuff', 'deleteme')
-        y1.delete('stuff')
-        y2.set('stuff', 'c1')
-        y3.set('stuff', 'c2')
-        y4.set('stuff', 'c3')
-        yield flushAll()
-
-        for (var key in this.users) {
-          var u = this.users[key]
-          expect(u.root.get('stuff')).toBeUndefined()
-        }
-        done()
-      }))
-      it('observePath properties', async(function * (done) {
-        y1.observePath(['map'], function (map) {
-          if (map != null) {
-            map.set('yay', 4)
-          }
-        })
-        yield y2.set('map', Y.Map)
-        yield flushAll()
-        var map = yield y3.get('map')
-        expect(map.get('yay')).toEqual(4)
-        done()
-      }))
-      it('throws add & update & delete events (with type and primitive content)', async(function * (done) {
-        var event
-        yield flushAll()
-        y1.observe(function (e) {
-          event = e // just put it on event, should be thrown synchronously anyway
-        })
-        y1.set('stuff', 4)
-        expect(event).toEqual([{
-          type: 'add',
-          object: y1,
-          name: 'stuff'
-        }])
-        // update, oldValue is in contents
-        yield y1.set('stuff', Y.Array)
-        expect(event).toEqual([{
-          type: 'update',
-          object: y1,
-          name: 'stuff',
-          oldValue: 4
-        }])
-        y1.get('stuff').then(function (replacedArray) {
-          // update, oldValue is in opContents
-          y1.set('stuff', 5)
-          var getYArray = event[0].oldValue
-          expect(typeof getYArray.constructor === 'function').toBeTruthy()
-          getYArray().then(function (array) {
-            expect(array).toEqual(replacedArray)
-
-            // delete
-            y1.delete('stuff')
-            expect(event).toEqual([{
-              type: 'delete',
-              name: 'stuff',
-              object: y1,
-              oldValue: 5
-            }])
-            done()
-          })
-        })
-      }))
-    })
-    describeManyTimes(repeatMapTeasts, `${numberOfYMapTests} Random tests`, function () {
-      var randomMapTransactions = [
-        function set (map) {
-          map.set('somekey', getRandomNumber())
-        },
-        function delete_ (map) {
-          map.delete('somekey')
-        }
-      ]
-      function compareMapValues (maps) {
-        var firstMap
-        for (var map of maps) {
-          var val = map.getPrimitive()
-          if (firstMap == null) {
-            firstMap = val
-          } else {
-            expect(val).toEqual(firstMap)
-          }
-        }
-      }
-      beforeEach(async(function * (done) {
-        yield y1.set('Map', Y.Map)
-        yield flushAll()
-
-        var promises = []
-        for (var u = 0; u < this.users.length; u++) {
-          promises.push(this.users[u].root.get('Map'))
-        }
-        this.maps = yield Promise.all(promises)
-        done()
-      }))
-      it(`succeed after ${numberOfYMapTests} actions, no GC, all users disconnecting/reconnecting`, async(function * (done) {
-        yield applyRandomTransactionsAllRejoinNoGC(this.users, this.maps, randomMapTransactions, numberOfYMapTests)
-        yield flushAll()
-        yield compareMapValues(this.maps)
-        done()
-      }))
-      it(`succeed after ${numberOfYMapTests} actions, GC, user[0] is not disconnecting`, async(function * (done) {
-        yield applyRandomTransactionsWithGC(this.users, this.maps, randomMapTransactions, numberOfYMapTests)
-        yield flushAll()
-        yield compareMapValues(this.maps)
-        done()
-      }))
-    })
-  })
-}
--- a/src/Types/TextBind.js
+++ b/src/Types/TextBind.js
@@ -1,290 +0,0 @@
-/* global Y */
-'use strict'
-
-;(function () {
-  class YTextBind extends Y.Array['class'] {
-    constructor (os, _model, idArray, valArray) {
-      super(os, _model, idArray, valArray)
-      this.textfields = []
-    }
-    toString () {
-      return this.valArray.join('')
-    }
-    insert (pos, content) {
-      super.insert(pos, content.split(''))
-    }
-    bind (textfield, domRoot) {
-      domRoot = domRoot || window; // eslint-disable-line
-      if (domRoot.getSelection == null) {
-        domRoot = window;// eslint-disable-line
-      }
-
-      // don't duplicate!
-      for (var t in this.textfields) {
-        if (this.textfields[t] === textfield) {
-          return
-        }
-      }
-      var creatorToken = false
-
-      var word = this
-      textfield.value = this.toString()
-      this.textfields.push(textfield)
-      var createRange, writeRange, writeContent
-      if (textfield.selectionStart != null && textfield.setSelectionRange != null) {
-        createRange = function (fix) {
-          var left = textfield.selectionStart
-          var right = textfield.selectionEnd
-          if (fix != null) {
-            left = fix(left)
-            right = fix(right)
-          }
-          return {
-            left: left,
-            right: right
-          }
-        }
-        writeRange = function (range) {
-          writeContent(word.toString())
-          textfield.setSelectionRange(range.left, range.right)
-        }
-        writeContent = function (content) {
-          textfield.value = content
-        }
-      } else {
-        createRange = function (fix) {
-          var range = {}
-          var s = domRoot.getSelection()
-          var clength = textfield.textContent.length
-          range.left = Math.min(s.anchorOffset, clength)
-          range.right = Math.min(s.focusOffset, clength)
-          if (fix != null) {
-            range.left = fix(range.left)
-            range.right = fix(range.right)
-          }
-          var editedElement = s.focusNode
-          if (editedElement === textfield || editedElement === textfield.childNodes[0]) {
-            range.isReal = true
-          } else {
-            range.isReal = false
-          }
-          return range
-        }
-
-        writeRange = function (range) {
-          writeContent(word.toString())
-          var textnode = textfield.childNodes[0]
-          if (range.isReal && textnode != null) {
-            if (range.left < 0) {
-              range.left = 0
-            }
-            range.right = Math.max(range.left, range.right)
-            if (range.right > textnode.length) {
-              range.right = textnode.length
-            }
-            range.left = Math.min(range.left, range.right)
-            var r = document.createRange(); // eslint-disable-line
-            r.setStart(textnode, range.left)
-            r.setEnd(textnode, range.right)
-            var s = window.getSelection(); // eslint-disable-line
-            s.removeAllRanges()
-            s.addRange(r)
-          }
-        }
-        writeContent = function (content) {
-          var contentArray = content.replace(new RegExp('\n', 'g'), ' ').split(' ');// eslint-disable-line
-          textfield.innerText = ''
-          for (var i in contentArray) {
-            var c = contentArray[i]
-            textfield.innerText += c
-            if (i !== contentArray.length - 1) {
-              textfield.innerHTML += '&nbsp;'
-            }
-          }
-        }
-      }
-      writeContent(this.toString())
-
-      this.observe(function (events) {
-        for (var e in events) {
-          var event = events[e]
-          if (!creatorToken) {
-            var oPos, fix
-            if (event.type === 'insert') {
-              oPos = event.index
-              fix = function (cursor) {// eslint-disable-line
-                if (cursor <= oPos) {
-                  return cursor
-                } else {
-                  cursor += 1
-                  return cursor
-                }
-              }
-              var r = createRange(fix)
-              writeRange(r)
-            } else if (event.type === 'delete') {
-              oPos = event.index
-              fix = function (cursor) {// eslint-disable-line
-                if (cursor < oPos) {
-                  return cursor
-                } else {
-                  cursor -= 1
-                  return cursor
-                }
-              }
-              r = createRange(fix)
-              writeRange(r)
-            }
-          }
-        }
-      })
-      // consume all text-insert changes.
-      textfield.onkeypress = function (event) {
-        if (word.is_deleted) {
-          // if word is deleted, do not do anything ever again
-          textfield.onkeypress = null
-          return true
-        }
-        creatorToken = true
-        var char
-        if (event.keyCode === 13) {
-          char = '\n'
-        } else if (event.key != null) {
-          if (event.charCode === 32) {
-            char = ' '
-          } else {
-            char = event.key
-          }
-        } else {
-          char = window.String.fromCharCode(event.keyCode); // eslint-disable-line
-        }
-        if (char.length > 1) {
-          return true
-        } else if (char.length > 0) {
-          var r = createRange()
-          var pos = Math.min(r.left, r.right, word.length)
-          var diff = Math.abs(r.right - r.left)
-          word.delete(pos, diff)
-          word.insert(pos, char)
-          r.left = pos + char.length
-          r.right = r.left
-          writeRange(r)
-        }
-        event.preventDefault()
-        creatorToken = false
-        return false
-      }
-      textfield.onpaste = function (event) {
-        if (word.is_deleted) {
-          // if word is deleted, do not do anything ever again
-          textfield.onpaste = null
-          return true
-        }
-        event.preventDefault()
-      }
-      textfield.oncut = function (event) {
-        if (word.is_deleted) {
-          // if word is deleted, do not do anything ever again
-          textfield.oncut = null
-          return true
-        }
-        event.preventDefault()
-      }
-      //
-      // consume deletes. Note that
-      //   chrome: won't consume deletions on keypress event.
-      //   keyCode is deprecated. BUT: I don't see another way.
-      //     since event.key is not implemented in the current version of chrome.
-      //     Every browser supports keyCode. Let's stick with it for now..
-      //
-      textfield.onkeydown = function (event) {
-        creatorToken = true
-        if (word.is_deleted) {
-          // if word is deleted, do not do anything ever again
-          textfield.onkeydown = null
-          return true
-        }
-        var r = createRange()
-        var pos = Math.min(r.left, r.right, word.toString().length)
-        var diff = Math.abs(r.left - r.right)
-        if (event.keyCode != null && event.keyCode === 8) { // Backspace
-          if (diff > 0) {
-            word.delete(pos, diff)
-            r.left = pos
-            r.right = pos
-            writeRange(r)
-          } else {
-            if (event.ctrlKey != null && event.ctrlKey) {
-              var val = word.toString()
-              var newPos = pos
-              var delLength = 0
-              if (pos > 0) {
-                newPos--
-                delLength++
-              }
-              while (newPos > 0 && val[newPos] !== ' ' && val[newPos] !== '\n') {
-                newPos--
-                delLength++
-              }
-              word.delete(newPos, pos - newPos)
-              r.left = newPos
-              r.right = newPos
-              writeRange(r)
-            } else {
-              if (pos > 0) {
-                word.delete(pos - 1, 1)
-                r.left = pos - 1
-                r.right = pos - 1
-                writeRange(r)
-              }
-            }
-          }
-          event.preventDefault()
-          creatorToken = false
-          return false
-        } else if (event.keyCode != null && event.keyCode === 46) { // Delete
-          if (diff > 0) {
-            word.delete(pos, diff)
-            r.left = pos
-            r.right = pos
-            writeRange(r)
-          } else {
-            word.delete(pos, 1)
-            r.left = pos
-            r.right = pos
-            writeRange(r)
-          }
-          event.preventDefault()
-          creatorToken = false
-          return false
-        } else {
-          creatorToken = false
-          return true
-        }
-      }
-    }
-  }
-  Y.TextBind = new Y.utils.CustomType({
-    class: YTextBind,
-    createType: function * YTextBindCreator () {
-      var modelid = this.store.getNextOpId()
-      var model = {
-        start: null,
-        end: null,
-        struct: 'List',
-        type: 'TextBind',
-        id: modelid
-      }
-      yield* this.applyCreatedOperations([model])
-      return modelid
-    },
-    initType: function * YTextBindInitializer (os, model) {
-      var valArray = []
-      var idArray = yield* Y.Struct.List.map.call(this, model, function (c) {
-        valArray.push(c.content)
-        return JSON.stringify(c.id)
-      })
-      return new YTextBind(os, model.id, idArray, valArray)
-    }
-  })
-})()
--- a/src/Utils.js
+++ b/src/Utils.js
@@ -1,198 +0,0 @@
-/* global Y */
-'use strict'
-
-/*
-  EventHandler is an helper class for constructing custom types.
-
-  Why: When constructing custom types, you sometimes want your types to work
-  synchronous: E.g.
-  ``` Synchronous
-  mytype.setSomething("yay")
-  mytype.getSomething() === "yay"
-  ```
-  ``` Asynchronous
-  mytype.setSomething("yay")
-  mytype.getSomething() === undefined
-  mytype.waitForSomething().then(function(){
-    mytype.getSomething() === "yay"
-  })
-
-  The structures usually work asynchronously (you have to wait for the
-  database request to finish). EventHandler will help you to make your type
-  synchronously.
-*/
-class EventHandler {
-  /*
-    onevent: is called when the structure changes.
-
-    Note: "awaiting opertations" is used to denote operations that were
-    prematurely called. Events for received operations can not be executed until
-    all prematurely called operations were executed ("waiting operations")
-  */
-  constructor (onevent) {
-    this.waiting = []
-    this.awaiting = 0
-    this.onevent = onevent
-    this.eventListeners = []
-  }
-  /*
-    Call this when a new operation arrives. It will be executed right away if
-    there are no waiting operations, that you prematurely executed
-  */
-  receivedOp (op) {
-    if (this.awaiting <= 0) {
-      this.onevent([op])
-    } else {
-      this.waiting.push(Y.utils.copyObject(op))
-    }
-  }
-  /*
-    You created some operations, and you want the `onevent` function to be
-    called right away. Received operations will not be executed untill all
-    prematurely called operations are executed
-  */
-  awaitAndPrematurelyCall (ops) {
-    this.awaiting++
-    this.onevent(ops)
-  }
-  /*
-    Basic event listener boilerplate...
-    TODO: maybe put this in a different type..
-  */
-  addEventListener (f) {
-    this.eventListeners.push(f)
-  }
-  removeEventListener (f) {
-    this.eventListeners = this.eventListeners.filter(function (g) {
-      return f !== g
-    })
-  }
-  removeAllEventListeners () {
-    this.eventListeners = []
-  }
-  callEventListeners (event) {
-    for (var i in this.eventListeners) {
-      try {
-        this.eventListeners[i](event)
-      } catch (e) {
-        console.log('User events must not throw Errors!') // eslint-disable-line
-      }
-    }
-  }
-  /*
-    Call this when you successfully awaited the execution of n Insert operations
-  */
-  awaitedInserts (n) {
-    var ops = this.waiting.splice(this.waiting.length - n)
-    for (var oid = 0; oid < ops.length; oid++) {
-      var op = ops[oid]
-      for (var i = this.waiting.length - 1; i >= 0; i--) {
-        let w = this.waiting[i]
-        if (Y.utils.compareIds(op.left, w.id)) {
-          // include the effect of op in w
-          w.right = op.id
-          // exclude the effect of w in op
-          op.left = w.left
-        } else if (Y.utils.compareIds(op.right, w.id)) {
-          // similar..
-          w.left = op.id
-          op.right = w.right
-        }
-      }
-    }
-    this._tryCallEvents()
-  }
-  /*
-    Call this when you successfully awaited the execution of n Delete operations
-  */
-  awaitedDeletes (n, newLeft) {
-    var ops = this.waiting.splice(this.waiting.length - n)
-    for (var j in ops) {
-      var del = ops[j]
-      if (newLeft != null) {
-        for (var i in this.waiting) {
-          let w = this.waiting[i]
-          // We will just care about w.left
-          if (Y.utils.compareIds(del.target, w.left)) {
-            del.left = newLeft
-          }
-        }
-      }
-    }
-    this._tryCallEvents()
-  }
-  /* (private)
-    Try to execute the events for the waiting operations
-  */
-  _tryCallEvents () {
-    this.awaiting--
-    if (this.awaiting <= 0 && this.waiting.length > 0) {
-      var events = this.waiting
-      this.waiting = []
-      this.onevent(events)
-    }
-  }
-}
-Y.utils.EventHandler = EventHandler
-
-/*
-  A wrapper for the definition of a custom type.
-  Every custom type must have three properties:
-
-  * createType
-    - Defines the model of a newly created custom type and returns the type
-  * initType
-    - Given a model, creates a custom type
-  * class
-    - the constructor of the custom type (e.g. in order to inherit from a type)
-*/
-class CustomType { // eslint-disable-line
-  constructor (def) {
-    if (def.createType == null ||
-      def.initType == null ||
-      def.class == null
-    ) {
-      throw new Error('Custom type was not initialized correctly!')
-    }
-    this.createType = def.createType
-    this.initType = def.initType
-    this.class = def.class
-  }
-}
-Y.utils.CustomType = CustomType
-
-/*
-  Make a flat copy of an object
-  (just copy properties)
-*/
-function copyObject (o) {
-  var c = {}
-  for (var key in o) {
-    c[key] = o[key]
-  }
-  return c
-}
-Y.utils.copyObject = copyObject
-
-/*
-  Defines a smaller relation on Id's
-*/
-function smaller (a, b) {
-  return a[0] < b[0] || (a[0] === b[0] && a[1] < b[1])
-}
-Y.utils.smaller = smaller
-
-function compareIds (id1, id2) {
-  if (id1 == null || id2 == null) {
-    if (id1 == null && id2 == null) {
-      return true
-    }
-    return false
-  }
-  if (id1[0] === id2[0] && id1[1] === id2[1]) {
-    return true
-  } else {
-    return false
-  }
-}
-Y.utils.compareIds = compareIds
--- a/src/index.js
+++ b/src/index.js
@@ -0,0 +1,109 @@
+/** eslint-env browser */
+
+export {
+  Doc,
+  Transaction,
+  YArray as Array,
+  YMap as Map,
+  YText as Text,
+  YXmlText as XmlText,
+  YXmlHook as XmlHook,
+  YXmlElement as XmlElement,
+  YXmlFragment as XmlFragment,
+  YXmlEvent,
+  YMapEvent,
+  YArrayEvent,
+  YTextEvent,
+  YEvent,
+  Item,
+  AbstractStruct,
+  GC,
+  ContentBinary,
+  ContentDeleted,
+  ContentEmbed,
+  ContentFormat,
+  ContentJSON,
+  ContentAny,
+  ContentString,
+  ContentType,
+  AbstractType,
+  RelativePosition,
+  getTypeChildren,
+  createRelativePositionFromTypeIndex,
+  createRelativePositionFromJSON,
+  createAbsolutePositionFromRelativePosition,
+  compareRelativePositions,
+  ID,
+  createID,
+  compareIDs,
+  getState,
+  Snapshot,
+  createSnapshot,
+  createDeleteSet,
+  createDeleteSetFromStructStore,
+  snapshot,
+  emptySnapshot,
+  findRootTypeKey,
+  findIndexSS,
+  getItem,
+  typeListToArraySnapshot,
+  typeMapGetSnapshot,
+  createDocFromSnapshot,
+  iterateDeletedStructs,
+  applyUpdate,
+  applyUpdateV2,
+  readUpdate,
+  readUpdateV2,
+  encodeStateAsUpdate,
+  encodeStateAsUpdateV2,
+  encodeStateVector,
+  UndoManager,
+  decodeSnapshot,
+  encodeSnapshot,
+  decodeSnapshotV2,
+  encodeSnapshotV2,
+  decodeStateVector,
+  logUpdate,
+  logUpdateV2,
+  relativePositionToJSON,
+  isDeleted,
+  isParentOf,
+  equalSnapshots,
+  PermanentUserData, // @TODO experimental
+  tryGc,
+  transact,
+  AbstractConnector,
+  logType,
+  mergeUpdates,
+  mergeUpdatesV2,
+  parseUpdateMeta,
+  parseUpdateMetaV2,
+  encodeStateVectorFromUpdate,
+  encodeStateVectorFromUpdateV2,
+  encodeRelativePosition,
+  decodeRelativePosition,
+  diffUpdate,
+  diffUpdateV2
+} from './internals.js'
+
+const glo = /** @type {any} */ (typeof window !== 'undefined'
+  ? window
+  : typeof global !== 'undefined' ? global : {})
+const importIdentifier = '__ $YJS$ __'
+
+if (glo[importIdentifier] === true) {
+  /**
+   * Dear reader of this warning message. Please take this seriously.
+   *
+   * If you see this message, please make sure that you only import one version of Yjs. In many cases,
+   * your package manager installs two versions of Yjs that are used by different packages within your project.
+   * Another reason for this message is that some parts of your project use the commonjs version of Yjs
+   * and others use the EcmaScript version of Yjs.
+   *
+   * This often leads to issues that are hard to debug. We often need to perform constructor checks,
+   * e.g. `struct instanceof GC`. If you imported different versions of Yjs, it is impossible for us to
+   * do the constructor checks anymore - which might break the CRDT algorithm.
+   */
+  console.warn('Yjs was already imported. Importing different versions of Yjs often leads to issues.')
+}
+glo[importIdentifier] = true
--- a/src/internals.js
+++ b/src/internals.js
@@ -0,0 +1,43 @@
+
+export * from './utils/AbstractConnector.js'
+export * from './utils/DeleteSet.js'
+export * from './utils/Doc.js'
+export * from './utils/UpdateDecoder.js'
+export * from './utils/UpdateEncoder.js'
+export * from './utils/encoding.js'
+export * from './utils/EventHandler.js'
+export * from './utils/ID.js'
+export * from './utils/isParentOf.js'
+export * from './utils/logging.js'
+export * from './utils/PermanentUserData.js'
+export * from './utils/RelativePosition.js'
+export * from './utils/Snapshot.js'
+export * from './utils/StructStore.js'
+export * from './utils/Transaction.js'
+export * from './utils/UndoManager.js'
+export * from './utils/updates.js'
+export * from './utils/YEvent.js'
+
+export * from './types/AbstractType.js'
+export * from './types/YArray.js'
+export * from './types/YMap.js'
+export * from './types/YText.js'
+export * from './types/YXmlFragment.js'
+export * from './types/YXmlElement.js'
+export * from './types/YXmlEvent.js'
+export * from './types/YXmlHook.js'
+export * from './types/YXmlText.js'
+
+export * from './structs/AbstractStruct.js'
+export * from './structs/GC.js'
+export * from './structs/ContentBinary.js'
+export * from './structs/ContentDeleted.js'
+export * from './structs/ContentDoc.js'
+export * from './structs/ContentEmbed.js'
+export * from './structs/ContentFormat.js'
+export * from './structs/ContentJSON.js'
+export * from './structs/ContentAny.js'
+export * from './structs/ContentString.js'
+export * from './structs/ContentType.js'
+export * from './structs/Item.js'
+export * from './structs/Skip.js'
--- a/src/structs/AbstractStruct.js
+++ b/src/structs/AbstractStruct.js
@@ -0,0 +1,52 @@
+
+import {
+  UpdateEncoderV1, UpdateEncoderV2, ID, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+export class AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {number} length
+   */
+  constructor (id, length) {
+    this.id = id
+    this.length = length
+  }
+
+  /**
+   * @type {boolean}
+   */
+  get deleted () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * Merge this struct with the item to the right.
+   * This method is already assuming that `this.id.clock + this.length === this.id.clock`.
+   * Also this method does *not* remove right from StructStore!
+   * @param {AbstractStruct} right
+   * @return {boolean} wether this merged with right
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   * @param {number} offset
+   * @param {number} encodingRef
+   */
+  write (encoder, offset, encodingRef) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    throw error.methodUnimplemented()
+  }
+}
--- a/src/structs/ContentAny.js
+++ b/src/structs/ContentAny.js
@@ -0,0 +1,108 @@
+import {
+  UpdateEncoderV1, UpdateEncoderV2, UpdateDecoderV1, UpdateDecoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+export class ContentAny {
+  /**
+   * @param {Array<any>} arr
+   */
+  constructor (arr) {
+    /**
+     * @type {Array<any>}
+     */
+    this.arr = arr
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.arr.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.arr
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentAny}
+   */
+  copy () {
+    return new ContentAny(this.arr)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentAny}
+   */
+  splice (offset) {
+    const right = new ContentAny(this.arr.slice(offset))
+    this.arr = this.arr.slice(0, offset)
+    return right
+  }
+
+  /**
+   * @param {ContentAny} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.arr = this.arr.concat(right.arr)
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoder.writeLen(len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoder.writeAny(c)
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 8
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentAny}
+ */
+export const readContentAny = decoder => {
+  const len = decoder.readLen()
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    cs.push(decoder.readAny())
+  }
+  return new ContentAny(cs)
+}
--- a/src/structs/ContentBinary.js
+++ b/src/structs/ContentBinary.js
@@ -0,0 +1,92 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+export class ContentBinary {
+  /**
+   * @param {Uint8Array} content
+   */
+  constructor (content) {
+    this.content = content
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.content]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentBinary}
+   */
+  copy () {
+    return new ContentBinary(this.content)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentBinary}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentBinary} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeBuf(this.content)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 3
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2 } decoder
+ * @return {ContentBinary}
+ */
+export const readContentBinary = decoder => new ContentBinary(decoder.readBuf())
--- a/src/structs/ContentDeleted.js
+++ b/src/structs/ContentDeleted.js
@@ -0,0 +1,101 @@
+
+import {
+  addToDeleteSet,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+export class ContentDeleted {
+  /**
+   * @param {number} len
+   */
+  constructor (len) {
+    this.len = len
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.len
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return []
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return false
+  }
+
+  /**
+   * @return {ContentDeleted}
+   */
+  copy () {
+    return new ContentDeleted(this.len)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentDeleted}
+   */
+  splice (offset) {
+    const right = new ContentDeleted(this.len - offset)
+    this.len = offset
+    return right
+  }
+
+  /**
+   * @param {ContentDeleted} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.len += right.len
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    addToDeleteSet(transaction.deleteSet, item.id.client, item.id.clock, this.len)
+    item.markDeleted()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeLen(this.len - offset)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 1
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2 } decoder
+ * @return {ContentDeleted}
+ */
+export const readContentDeleted = decoder => new ContentDeleted(decoder.readLen())
--- a/src/structs/ContentDoc.js
+++ b/src/structs/ContentDoc.js
@@ -0,0 +1,135 @@
+
+import {
+  Doc, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @private
+ */
+export class ContentDoc {
+  /**
+   * @param {Doc} doc
+   */
+  constructor (doc) {
+    if (doc._item) {
+      console.error('This document was already integrated as a sub-document. You should create a second instance instead with the same guid.')
+    }
+    /**
+     * @type {Doc}
+     */
+    this.doc = doc
+    /**
+     * @type {any}
+     */
+    const opts = {}
+    this.opts = opts
+    if (!doc.gc) {
+      opts.gc = false
+    }
+    if (doc.autoLoad) {
+      opts.autoLoad = true
+    }
+    if (doc.meta !== null) {
+      opts.meta = doc.meta
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.doc]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentDoc}
+   */
+  copy () {
+    return new ContentDoc(this.doc)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentDoc}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentDoc} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    // this needs to be reflected in doc.destroy as well
+    this.doc._item = item
+    transaction.subdocsAdded.add(this.doc)
+    if (this.doc.shouldLoad) {
+      transaction.subdocsLoaded.add(this.doc)
+    }
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    if (transaction.subdocsAdded.has(this.doc)) {
+      transaction.subdocsAdded.delete(this.doc)
+    } else {
+      transaction.subdocsRemoved.add(this.doc)
+    }
+  }
+
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) { }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeString(this.doc.guid)
+    encoder.writeAny(this.opts)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 9
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentDoc}
+ */
+export const readContentDoc = decoder => new ContentDoc(new Doc({ guid: decoder.readString(), ...decoder.readAny() }))
--- a/src/structs/ContentEmbed.js
+++ b/src/structs/ContentEmbed.js
@@ -0,0 +1,98 @@
+
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @private
+ */
+export class ContentEmbed {
+  /**
+   * @param {Object} embed
+   */
+  constructor (embed) {
+    this.embed = embed
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.embed]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentEmbed}
+   */
+  copy () {
+    return new ContentEmbed(this.embed)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentEmbed}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentEmbed} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeJSON(this.embed)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 5
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentEmbed}
+ */
+export const readContentEmbed = decoder => new ContentEmbed(decoder.readJSON())
--- a/src/structs/ContentFormat.js
+++ b/src/structs/ContentFormat.js
@@ -0,0 +1,103 @@
+
+import {
+  AbstractType, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Item, StructStore, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @private
+ */
+export class ContentFormat {
+  /**
+   * @param {string} key
+   * @param {Object} value
+   */
+  constructor (key, value) {
+    this.key = key
+    this.value = value
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return []
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return false
+  }
+
+  /**
+   * @return {ContentFormat}
+   */
+  copy () {
+    return new ContentFormat(this.key, this.value)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentFormat}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentFormat} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    // @todo searchmarker are currently unsupported for rich text documents
+    /** @type {AbstractType<any>} */ (item.parent)._searchMarker = null
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeKey(this.key)
+    encoder.writeJSON(this.value)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 6
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentFormat}
+ */
+export const readContentFormat = decoder => new ContentFormat(decoder.readString(), decoder.readJSON())
--- a/src/structs/ContentJSON.js
+++ b/src/structs/ContentJSON.js
@@ -0,0 +1,118 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @private
+ */
+export class ContentJSON {
+  /**
+   * @param {Array<any>} arr
+   */
+  constructor (arr) {
+    /**
+     * @type {Array<any>}
+     */
+    this.arr = arr
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.arr.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.arr
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentJSON}
+   */
+  copy () {
+    return new ContentJSON(this.arr)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentJSON}
+   */
+  splice (offset) {
+    const right = new ContentJSON(this.arr.slice(offset))
+    this.arr = this.arr.slice(0, offset)
+    return right
+  }
+
+  /**
+   * @param {ContentJSON} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.arr = this.arr.concat(right.arr)
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoder.writeLen(len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoder.writeString(c === undefined ? 'undefined' : JSON.stringify(c))
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 2
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentJSON}
+ */
+export const readContentJSON = decoder => {
+  const len = decoder.readLen()
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    const c = decoder.readString()
+    if (c === 'undefined') {
+      cs.push(undefined)
+    } else {
+      cs.push(JSON.parse(c))
+    }
+  }
+  return new ContentJSON(cs)
+}
--- a/src/structs/ContentString.js
+++ b/src/structs/ContentString.js
@@ -0,0 +1,112 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @private
+ */
+export class ContentString {
+  /**
+   * @param {string} str
+   */
+  constructor (str) {
+    /**
+     * @type {string}
+     */
+    this.str = str
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.str.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.str.split('')
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentString}
+   */
+  copy () {
+    return new ContentString(this.str)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentString}
+   */
+  splice (offset) {
+    const right = new ContentString(this.str.slice(offset))
+    this.str = this.str.slice(0, offset)
+
+    // Prevent encoding invalid documents because of splitting of surrogate pairs: https://github.com/yjs/yjs/issues/248
+    const firstCharCode = this.str.charCodeAt(offset - 1)
+    if (firstCharCode >= 0xD800 && firstCharCode <= 0xDBFF) {
+      // Last character of the left split is the start of a surrogate utf16/ucs2 pair.
+      // We don't support splitting of surrogate pairs because this may lead to invalid documents.
+      // Replace the invalid character with a unicode replacement character (<28> / U+FFFD)
+      this.str = this.str.slice(0, offset - 1) + '<27>'
+      // replace right as well
+      right.str = '<27>' + right.str.slice(1)
+    }
+    return right
+  }
+
+  /**
+   * @param {ContentString} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.str += right.str
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeString(offset === 0 ? this.str : this.str.slice(offset))
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 4
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentString}
+ */
+export const readContentString = decoder => new ContentString(decoder.readString())
--- a/src/structs/ContentType.js
+++ b/src/structs/ContentType.js
@@ -0,0 +1,172 @@
+
+import {
+  readYArray,
+  readYMap,
+  readYText,
+  readYXmlElement,
+  readYXmlFragment,
+  readYXmlHook,
+  readYXmlText,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, Item, YEvent, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @type {Array<function(UpdateDecoderV1 | UpdateDecoderV2):AbstractType<any>>}
+ * @private
+ */
+export const typeRefs = [
+  readYArray,
+  readYMap,
+  readYText,
+  readYXmlElement,
+  readYXmlFragment,
+  readYXmlHook,
+  readYXmlText
+]
+
+export const YArrayRefID = 0
+export const YMapRefID = 1
+export const YTextRefID = 2
+export const YXmlElementRefID = 3
+export const YXmlFragmentRefID = 4
+export const YXmlHookRefID = 5
+export const YXmlTextRefID = 6
+
+/**
+ * @private
+ */
+export class ContentType {
+  /**
+   * @param {AbstractType<YEvent>} type
+   */
+  constructor (type) {
+    /**
+     * @type {AbstractType<any>}
+     */
+    this.type = type
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.type]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentType}
+   */
+  copy () {
+    return new ContentType(this.type._copy())
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentType}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentType} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    this.type._integrate(transaction.doc, item)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    let item = this.type._start
+    while (item !== null) {
+      if (!item.deleted) {
+        item.delete(transaction)
+      } else {
+        // Whis will be gc'd later and we want to merge it if possible
+        // We try to merge all deleted items after each transaction,
+        // but we have no knowledge about that this needs to be merged
+        // since it is not in transaction.ds. Hence we add it to transaction._mergeStructs
+        transaction._mergeStructs.push(item)
+      }
+      item = item.right
+    }
+    this.type._map.forEach(item => {
+      if (!item.deleted) {
+        item.delete(transaction)
+      } else {
+        // same as above
+        transaction._mergeStructs.push(item)
+      }
+    })
+    transaction.changed.delete(this.type)
+  }
+
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {
+    let item = this.type._start
+    while (item !== null) {
+      item.gc(store, true)
+      item = item.right
+    }
+    this.type._start = null
+    this.type._map.forEach(/** @param {Item | null} item */ (item) => {
+      while (item !== null) {
+        item.gc(store, true)
+        item = item.left
+      }
+    })
+    this.type._map = new Map()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    this.type._write(encoder)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 7
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentType}
+ */
+export const readContentType = decoder => new ContentType(typeRefs[decoder.readTypeRef()](decoder))
--- a/src/structs/GC.js
+++ b/src/structs/GC.js
@@ -0,0 +1,61 @@
+
+import {
+  AbstractStruct,
+  addStruct,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+export const structGCRefNumber = 0
+
+/**
+ * @private
+ */
+export class GC extends AbstractStruct {
+  get deleted () {
+    return true
+  }
+
+  delete () {}
+
+  /**
+   * @param {GC} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (this.constructor !== right.constructor) {
+      return false
+    }
+    this.length += right.length
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    if (offset > 0) {
+      this.id.clock += offset
+      this.length -= offset
+    }
+    addStruct(transaction.doc.store, this)
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeInfo(structGCRefNumber)
+    encoder.writeLen(this.length - offset)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    return null
+  }
+}
--- a/src/structs/Item.js
+++ b/src/structs/Item.js
@@ -0,0 +1,806 @@
+
+import {
+  GC,
+  getState,
+  AbstractStruct,
+  replaceStruct,
+  addStruct,
+  addToDeleteSet,
+  findRootTypeKey,
+  compareIDs,
+  getItem,
+  getItemCleanEnd,
+  getItemCleanStart,
+  readContentDeleted,
+  readContentBinary,
+  readContentJSON,
+  readContentAny,
+  readContentString,
+  readContentEmbed,
+  readContentDoc,
+  createID,
+  readContentFormat,
+  readContentType,
+  addChangedTypeToTransaction,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, ContentType, ContentDeleted, StructStore, ID, AbstractType, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+import * as binary from 'lib0/binary'
+
+/**
+ * @todo This should return several items
+ *
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {{item:Item, diff:number}}
+ */
+export const followRedone = (store, id) => {
+  /**
+   * @type {ID|null}
+   */
+  let nextID = id
+  let diff = 0
+  let item
+  do {
+    if (diff > 0) {
+      nextID = createID(nextID.client, nextID.clock + diff)
+    }
+    item = getItem(store, nextID)
+    diff = nextID.clock - item.id.clock
+    nextID = item.redone
+  } while (nextID !== null && item instanceof Item)
+  return {
+    item, diff
+  }
+}
+
+/**
+ * Make sure that neither item nor any of its parents is ever deleted.
+ *
+ * This property does not persist when storing it into a database or when
+ * sending it to other peers
+ *
+ * @param {Item|null} item
+ * @param {boolean} keep
+ */
+export const keepItem = (item, keep) => {
+  while (item !== null && item.keep !== keep) {
+    item.keep = keep
+    item = /** @type {AbstractType<any>} */ (item.parent)._item
+  }
+}
+
+/**
+ * Split leftItem into two items
+ * @param {Transaction} transaction
+ * @param {Item} leftItem
+ * @param {number} diff
+ * @return {Item}
+ *
+ * @function
+ * @private
+ */
+export const splitItem = (transaction, leftItem, diff) => {
+  // create rightItem
+  const { client, clock } = leftItem.id
+  const rightItem = new Item(
+    createID(client, clock + diff),
+    leftItem,
+    createID(client, clock + diff - 1),
+    leftItem.right,
+    leftItem.rightOrigin,
+    leftItem.parent,
+    leftItem.parentSub,
+    leftItem.content.splice(diff)
+  )
+  if (leftItem.deleted) {
+    rightItem.markDeleted()
+  }
+  if (leftItem.keep) {
+    rightItem.keep = true
+  }
+  if (leftItem.redone !== null) {
+    rightItem.redone = createID(leftItem.redone.client, leftItem.redone.clock + diff)
+  }
+  // update left (do not set leftItem.rightOrigin as it will lead to problems when syncing)
+  leftItem.right = rightItem
+  // update right
+  if (rightItem.right !== null) {
+    rightItem.right.left = rightItem
+  }
+  // right is more specific.
+  transaction._mergeStructs.push(rightItem)
+  // update parent._map
+  if (rightItem.parentSub !== null && rightItem.right === null) {
+    /** @type {AbstractType<any>} */ (rightItem.parent)._map.set(rightItem.parentSub, rightItem)
+  }
+  leftItem.length = diff
+  return rightItem
+}
+
+/**
+ * Redoes the effect of this operation.
+ *
+ * @param {Transaction} transaction The Yjs instance.
+ * @param {Item} item
+ * @param {Set<Item>} redoitems
+ * @param {Array<Item>} itemsToDelete
+ *
+ * @return {Item|null}
+ *
+ * @private
+ */
+export const redoItem = (transaction, item, redoitems, itemsToDelete) => {
+  const doc = transaction.doc
+  const store = doc.store
+  const ownClientID = doc.clientID
+  const redone = item.redone
+  if (redone !== null) {
+    return getItemCleanStart(transaction, redone)
+  }
+  let parentItem = /** @type {AbstractType<any>} */ (item.parent)._item
+  /**
+   * @type {Item|null}
+   */
+  let left
+  /**
+   * @type {Item|null}
+   */
+  let right
+  if (item.parentSub === null) {
+    // Is an array item. Insert at the old position
+    left = item.left
+    right = item
+  } else {
+    // Is a map item. Insert as current value
+    left = item
+    while (left.right !== null) {
+      left = left.right
+      if (left.id.client !== ownClientID) {
+        // It is not possible to redo this item because it conflicts with a
+        // change from another client
+        return null
+      }
+    }
+    if (left.right !== null) {
+      left = /** @type {Item} */ (/** @type {AbstractType<any>} */ (item.parent)._map.get(item.parentSub))
+    }
+    right = null
+  }
+  // make sure that parent is redone
+  if (parentItem !== null && parentItem.deleted === true && parentItem.redone === null) {
+    // try to undo parent if it will be undone anyway
+    if (!redoitems.has(parentItem) || redoItem(transaction, parentItem, redoitems, itemsToDelete) === null) {
+      return null
+    }
+  }
+  if (parentItem !== null && parentItem.redone !== null) {
+    while (parentItem.redone !== null) {
+      parentItem = getItemCleanStart(transaction, parentItem.redone)
+    }
+    // find next cloned_redo items
+    while (left !== null) {
+      /**
+       * @type {Item|null}
+       */
+      let leftTrace = left
+      // trace redone until parent matches
+      while (leftTrace !== null && /** @type {AbstractType<any>} */ (leftTrace.parent)._item !== parentItem) {
+        leftTrace = leftTrace.redone === null ? null : getItemCleanStart(transaction, leftTrace.redone)
+      }
+      if (leftTrace !== null && /** @type {AbstractType<any>} */ (leftTrace.parent)._item === parentItem) {
+        left = leftTrace
+        break
+      }
+      left = left.left
+    }
+    while (right !== null) {
+      /**
+       * @type {Item|null}
+       */
+      let rightTrace = right
+      // trace redone until parent matches
+      while (rightTrace !== null && /** @type {AbstractType<any>} */ (rightTrace.parent)._item !== parentItem) {
+        rightTrace = rightTrace.redone === null ? null : getItemCleanStart(transaction, rightTrace.redone)
+      }
+      if (rightTrace !== null && /** @type {AbstractType<any>} */ (rightTrace.parent)._item === parentItem) {
+        right = rightTrace
+        break
+      }
+      right = right.right
+    }
+    // Iterate right while right is in itemsToDelete
+    // If it is intended to delete right while item is redone, we can expect that item should replace right.
+    while (left !== null && left.right !== null && left.right !== right && itemsToDelete.findIndex(d => d === /** @type {Item} */ (left).right) >= 0) {
+      left = left.right
+    }
+  }
+  const nextClock = getState(store, ownClientID)
+  const nextId = createID(ownClientID, nextClock)
+  const redoneItem = new Item(
+    nextId,
+    left, left && left.lastId,
+    right, right && right.id,
+    parentItem === null ? item.parent : /** @type {ContentType} */ (parentItem.content).type,
+    item.parentSub,
+    item.content.copy()
+  )
+  item.redone = nextId
+  keepItem(redoneItem, true)
+  redoneItem.integrate(transaction, 0)
+  return redoneItem
+}
+
+/**
+ * Abstract class that represents any content.
+ */
+export class Item extends AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {Item | null} left
+   * @param {ID | null} origin
+   * @param {Item | null} right
+   * @param {ID | null} rightOrigin
+   * @param {AbstractType<any>|ID|null} parent Is a type if integrated, is null if it is possible to copy parent from left or right, is ID before integration to search for it.
+   * @param {string | null} parentSub
+   * @param {AbstractContent} content
+   */
+  constructor (id, left, origin, right, rightOrigin, parent, parentSub, content) {
+    super(id, content.getLength())
+    /**
+     * The item that was originally to the left of this item.
+     * @type {ID | null}
+     */
+    this.origin = origin
+    /**
+     * The item that is currently to the left of this item.
+     * @type {Item | null}
+     */
+    this.left = left
+    /**
+     * The item that is currently to the right of this item.
+     * @type {Item | null}
+     */
+    this.right = right
+    /**
+     * The item that was originally to the right of this item.
+     * @type {ID | null}
+     */
+    this.rightOrigin = rightOrigin
+    /**
+     * @type {AbstractType<any>|ID|null}
+     */
+    this.parent = parent
+    /**
+     * If the parent refers to this item with some kind of key (e.g. YMap, the
+     * key is specified here. The key is then used to refer to the list in which
+     * to insert this item. If `parentSub = null` type._start is the list in
+     * which to insert to. Otherwise it is `parent._map`.
+     * @type {String | null}
+     */
+    this.parentSub = parentSub
+    /**
+     * If this type's effect is reundone this type refers to the type that undid
+     * this operation.
+     * @type {ID | null}
+     */
+    this.redone = null
+    /**
+     * @type {AbstractContent}
+     */
+    this.content = content
+    /**
+     * bit1: keep
+     * bit2: countable
+     * bit3: deleted
+     * bit4: mark - mark node as fast-search-marker
+     * @type {number} byte
+     */
+    this.info = this.content.isCountable() ? binary.BIT2 : 0
+  }
+
+  /**
+   * This is used to mark the item as an indexed fast-search marker
+   *
+   * @type {boolean}
+   */
+  set marker (isMarked) {
+    if (((this.info & binary.BIT4) > 0) !== isMarked) {
+      this.info ^= binary.BIT4
+    }
+  }
+
+  get marker () {
+    return (this.info & binary.BIT4) > 0
+  }
+
+  /**
+   * If true, do not garbage collect this Item.
+   */
+  get keep () {
+    return (this.info & binary.BIT1) > 0
+  }
+
+  set keep (doKeep) {
+    if (this.keep !== doKeep) {
+      this.info ^= binary.BIT1
+    }
+  }
+
+  get countable () {
+    return (this.info & binary.BIT2) > 0
+  }
+
+  /**
+   * Whether this item was deleted or not.
+   * @type {Boolean}
+   */
+  get deleted () {
+    return (this.info & binary.BIT3) > 0
+  }
+
+  set deleted (doDelete) {
+    if (this.deleted !== doDelete) {
+      this.info ^= binary.BIT3
+    }
+  }
+
+  markDeleted () {
+    this.info |= binary.BIT3
+  }
+
+  /**
+   * Return the creator clientID of the missing op or define missing items and return null.
+   *
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    if (this.origin && this.origin.client !== this.id.client && this.origin.clock >= getState(store, this.origin.client)) {
+      return this.origin.client
+    }
+    if (this.rightOrigin && this.rightOrigin.client !== this.id.client && this.rightOrigin.clock >= getState(store, this.rightOrigin.client)) {
+      return this.rightOrigin.client
+    }
+    if (this.parent && this.parent.constructor === ID && this.id.client !== this.parent.client && this.parent.clock >= getState(store, this.parent.client)) {
+      return this.parent.client
+    }
+
+    // We have all missing ids, now find the items
+
+    if (this.origin) {
+      this.left = getItemCleanEnd(transaction, store, this.origin)
+      this.origin = this.left.lastId
+    }
+    if (this.rightOrigin) {
+      this.right = getItemCleanStart(transaction, this.rightOrigin)
+      this.rightOrigin = this.right.id
+    }
+    if ((this.left && this.left.constructor === GC) || (this.right && this.right.constructor === GC)) {
+      this.parent = null
+    }
+    // only set parent if this shouldn't be garbage collected
+    if (!this.parent) {
+      if (this.left && this.left.constructor === Item) {
+        this.parent = this.left.parent
+        this.parentSub = this.left.parentSub
+      }
+      if (this.right && this.right.constructor === Item) {
+        this.parent = this.right.parent
+        this.parentSub = this.right.parentSub
+      }
+    } else if (this.parent.constructor === ID) {
+      const parentItem = getItem(store, this.parent)
+      if (parentItem.constructor === GC) {
+        this.parent = null
+      } else {
+        this.parent = /** @type {ContentType} */ (parentItem.content).type
+      }
+    }
+    return null
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    if (offset > 0) {
+      this.id.clock += offset
+      this.left = getItemCleanEnd(transaction, transaction.doc.store, createID(this.id.client, this.id.clock - 1))
+      this.origin = this.left.lastId
+      this.content = this.content.splice(offset)
+      this.length -= offset
+    }
+
+    if (this.parent) {
+      if ((!this.left && (!this.right || this.right.left !== null)) || (this.left && this.left.right !== this.right)) {
+        /**
+         * @type {Item|null}
+         */
+        let left = this.left
+
+        /**
+         * @type {Item|null}
+         */
+        let o
+        // set o to the first conflicting item
+        if (left !== null) {
+          o = left.right
+        } else if (this.parentSub !== null) {
+          o = /** @type {AbstractType<any>} */ (this.parent)._map.get(this.parentSub) || null
+          while (o !== null && o.left !== null) {
+            o = o.left
+          }
+        } else {
+          o = /** @type {AbstractType<any>} */ (this.parent)._start
+        }
+        // TODO: use something like DeleteSet here (a tree implementation would be best)
+        // @todo use global set definitions
+        /**
+         * @type {Set<Item>}
+         */
+        const conflictingItems = new Set()
+        /**
+         * @type {Set<Item>}
+         */
+        const itemsBeforeOrigin = new Set()
+        // Let c in conflictingItems, b in itemsBeforeOrigin
+        // ***{origin}bbbb{this}{c,b}{c,b}{o}***
+        // Note that conflictingItems is a subset of itemsBeforeOrigin
+        while (o !== null && o !== this.right) {
+          itemsBeforeOrigin.add(o)
+          conflictingItems.add(o)
+          if (compareIDs(this.origin, o.origin)) {
+            // case 1
+            if (o.id.client < this.id.client) {
+              left = o
+              conflictingItems.clear()
+            } else if (compareIDs(this.rightOrigin, o.rightOrigin)) {
+              // this and o are conflicting and point to the same integration points. The id decides which item comes first.
+              // Since this is to the left of o, we can break here
+              break
+            } // else, o might be integrated before an item that this conflicts with. If so, we will find it in the next iterations
+          } else if (o.origin !== null && itemsBeforeOrigin.has(getItem(transaction.doc.store, o.origin))) { // use getItem instead of getItemCleanEnd because we don't want / need to split items.
+            // case 2
+            if (!conflictingItems.has(getItem(transaction.doc.store, o.origin))) {
+              left = o
+              conflictingItems.clear()
+            }
+          } else {
+            break
+          }
+          o = o.right
+        }
+        this.left = left
+      }
+      // reconnect left/right + update parent map/start if necessary
+      if (this.left !== null) {
+        const right = this.left.right
+        this.right = right
+        this.left.right = this
+      } else {
+        let r
+        if (this.parentSub !== null) {
+          r = /** @type {AbstractType<any>} */ (this.parent)._map.get(this.parentSub) || null
+          while (r !== null && r.left !== null) {
+            r = r.left
+          }
+        } else {
+          r = /** @type {AbstractType<any>} */ (this.parent)._start
+          ;/** @type {AbstractType<any>} */ (this.parent)._start = this
+        }
+        this.right = r
+      }
+      if (this.right !== null) {
+        this.right.left = this
+      } else if (this.parentSub !== null) {
+        // set as current parent value if right === null and this is parentSub
+        /** @type {AbstractType<any>} */ (this.parent)._map.set(this.parentSub, this)
+        if (this.left !== null) {
+          // this is the current attribute value of parent. delete right
+          this.left.delete(transaction)
+        }
+      }
+      // adjust length of parent
+      if (this.parentSub === null && this.countable && !this.deleted) {
+        /** @type {AbstractType<any>} */ (this.parent)._length += this.length
+      }
+      addStruct(transaction.doc.store, this)
+      this.content.integrate(transaction, this)
+      // add parent to transaction.changed
+      addChangedTypeToTransaction(transaction, /** @type {AbstractType<any>} */ (this.parent), this.parentSub)
+      if ((/** @type {AbstractType<any>} */ (this.parent)._item !== null && /** @type {AbstractType<any>} */ (this.parent)._item.deleted) || (this.parentSub !== null && this.right !== null)) {
+        // delete if parent is deleted or if this is not the current attribute value of parent
+        this.delete(transaction)
+      }
+    } else {
+      // parent is not defined. Integrate GC struct instead
+      new GC(this.id, this.length).integrate(transaction, 0)
+    }
+  }
+
+  /**
+   * Returns the next non-deleted item
+   */
+  get next () {
+    let n = this.right
+    while (n !== null && n.deleted) {
+      n = n.right
+    }
+    return n
+  }
+
+  /**
+   * Returns the previous non-deleted item
+   */
+  get prev () {
+    let n = this.left
+    while (n !== null && n.deleted) {
+      n = n.left
+    }
+    return n
+  }
+
+  /**
+   * Computes the last content address of this Item.
+   */
+  get lastId () {
+    // allocating ids is pretty costly because of the amount of ids created, so we try to reuse whenever possible
+    return this.length === 1 ? this.id : createID(this.id.client, this.id.clock + this.length - 1)
+  }
+
+  /**
+   * Try to merge two items
+   *
+   * @param {Item} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (
+      this.constructor === right.constructor &&
+      compareIDs(right.origin, this.lastId) &&
+      this.right === right &&
+      compareIDs(this.rightOrigin, right.rightOrigin) &&
+      this.id.client === right.id.client &&
+      this.id.clock + this.length === right.id.clock &&
+      this.deleted === right.deleted &&
+      this.redone === null &&
+      right.redone === null &&
+      this.content.constructor === right.content.constructor &&
+      this.content.mergeWith(right.content)
+    ) {
+      const searchMarker = /** @type {AbstractType<any>} */ (this.parent)._searchMarker
+      if (searchMarker) {
+        searchMarker.forEach(marker => {
+          if (marker.p === right) {
+            // right is going to be "forgotten" so we need to update the marker
+            marker.p = this
+            // adjust marker index
+            if (!this.deleted && this.countable) {
+              marker.index -= this.length
+            }
+          }
+        })
+      }
+      if (right.keep) {
+        this.keep = true
+      }
+      this.right = right.right
+      if (this.right !== null) {
+        this.right.left = this
+      }
+      this.length += right.length
+      return true
+    }
+    return false
+  }
+
+  /**
+   * Mark this Item as deleted.
+   *
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    if (!this.deleted) {
+      const parent = /** @type {AbstractType<any>} */ (this.parent)
+      // adjust the length of parent
+      if (this.countable && this.parentSub === null) {
+        parent._length -= this.length
+      }
+      this.markDeleted()
+      addToDeleteSet(transaction.deleteSet, this.id.client, this.id.clock, this.length)
+      addChangedTypeToTransaction(transaction, parent, this.parentSub)
+      this.content.delete(transaction)
+    }
+  }
+
+  /**
+   * @param {StructStore} store
+   * @param {boolean} parentGCd
+   */
+  gc (store, parentGCd) {
+    if (!this.deleted) {
+      throw error.unexpectedCase()
+    }
+    this.content.gc(store)
+    if (parentGCd) {
+      replaceStruct(store, this, new GC(this.id, this.length))
+    } else {
+      this.content = new ContentDeleted(this.length)
+    }
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const origin = offset > 0 ? createID(this.id.client, this.id.clock + offset - 1) : this.origin
+    const rightOrigin = this.rightOrigin
+    const parentSub = this.parentSub
+    const info = (this.content.getRef() & binary.BITS5) |
+      (origin === null ? 0 : binary.BIT8) | // origin is defined
+      (rightOrigin === null ? 0 : binary.BIT7) | // right origin is defined
+      (parentSub === null ? 0 : binary.BIT6) // parentSub is non-null
+    encoder.writeInfo(info)
+    if (origin !== null) {
+      encoder.writeLeftID(origin)
+    }
+    if (rightOrigin !== null) {
+      encoder.writeRightID(rightOrigin)
+    }
+    if (origin === null && rightOrigin === null) {
+      const parent = /** @type {AbstractType<any>} */ (this.parent)
+      if (parent._item !== undefined) {
+        const parentItem = parent._item
+        if (parentItem === null) {
+          // parent type on y._map
+          // find the correct key
+          const ykey = findRootTypeKey(parent)
+          encoder.writeParentInfo(true) // write parentYKey
+          encoder.writeString(ykey)
+        } else {
+          encoder.writeParentInfo(false) // write parent id
+          encoder.writeLeftID(parentItem.id)
+        }
+      } else if (parent.constructor === String) { // this edge case was added by differential updates
+        encoder.writeParentInfo(true) // write parentYKey
+        encoder.writeString(parent)
+      } else if (parent.constructor === ID) {
+        encoder.writeParentInfo(false) // write parent id
+        encoder.writeLeftID(parent)
+      } else {
+        error.unexpectedCase()
+      }
+      if (parentSub !== null) {
+        encoder.writeString(parentSub)
+      }
+    }
+    this.content.write(encoder, offset)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @param {number} info
+ */
+export const readItemContent = (decoder, info) => contentRefs[info & binary.BITS5](decoder)
+
+/**
+ * A lookup map for reading Item content.
+ *
+ * @type {Array<function(UpdateDecoderV1 | UpdateDecoderV2):AbstractContent>}
+ */
+export const contentRefs = [
+  () => { error.unexpectedCase() }, // GC is not ItemContent
+  readContentDeleted, // 1
+  readContentJSON, // 2
+  readContentBinary, // 3
+  readContentString, // 4
+  readContentEmbed, // 5
+  readContentFormat, // 6
+  readContentType, // 7
+  readContentAny, // 8
+  readContentDoc, // 9
+  () => { error.unexpectedCase() } // 10 - Skip is not ItemContent
+]
+
+/**
+ * Do not implement this class!
+ */
+export class AbstractContent {
+  /**
+   * @return {number}
+   */
+  getLength () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * Should return false if this Item is some kind of meta information
+   * (e.g. format information).
+   *
+   * * Whether this Item should be addressable via `yarray.get(i)`
+   * * Whether this Item should be counted when computing yarray.length
+   *
+   * @return {boolean}
+   */
+  isCountable () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {AbstractContent}
+   */
+  copy () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {number} offset
+   * @return {AbstractContent}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {AbstractContent} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    throw error.methodUnimplemented()
+  }
+}
--- a/src/structs/Skip.js
+++ b/src/structs/Skip.js
@@ -0,0 +1,60 @@
+
+import {
+  AbstractStruct,
+  UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+import * as error from 'lib0/error'
+import * as encoding from 'lib0/encoding'
+
+export const structSkipRefNumber = 10
+
+/**
+ * @private
+ */
+export class Skip extends AbstractStruct {
+  get deleted () {
+    return true
+  }
+
+  delete () {}
+
+  /**
+   * @param {Skip} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (this.constructor !== right.constructor) {
+      return false
+    }
+    this.length += right.length
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    // skip structs cannot be integrated
+    error.unexpectedCase()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeInfo(structSkipRefNumber)
+    // write as VarUint because Skips can't make use of predictable length-encoding
+    encoding.writeVarUint(encoder.restEncoder, this.length - offset)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    return null
+  }
+}
--- a/src/types/AbstractType.js
+++ b/src/types/AbstractType.js
@@ -0,0 +1,912 @@
+
+import {
+  removeEventHandlerListener,
+  callEventHandlerListeners,
+  addEventHandlerListener,
+  createEventHandler,
+  getState,
+  isVisible,
+  ContentType,
+  createID,
+  ContentAny,
+  ContentBinary,
+  getItemCleanStart,
+  ContentDoc, YText, YArray, UpdateEncoderV1, UpdateEncoderV2, Doc, Snapshot, Transaction, EventHandler, YEvent, Item, // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as iterator from 'lib0/iterator'
+import * as error from 'lib0/error'
+import * as math from 'lib0/math'
+
+const maxSearchMarker = 80
+
+/**
+ * A unique timestamp that identifies each marker.
+ *
+ * Time is relative,.. this is more like an ever-increasing clock.
+ *
+ * @type {number}
+ */
+let globalSearchMarkerTimestamp = 0
+
+export class ArraySearchMarker {
+  /**
+   * @param {Item} p
+   * @param {number} index
+   */
+  constructor (p, index) {
+    p.marker = true
+    this.p = p
+    this.index = index
+    this.timestamp = globalSearchMarkerTimestamp++
+  }
+}
+
+/**
+ * @param {ArraySearchMarker} marker
+ */
+const refreshMarkerTimestamp = marker => { marker.timestamp = globalSearchMarkerTimestamp++ }
+
+/**
+ * This is rather complex so this function is the only thing that should overwrite a marker
+ *
+ * @param {ArraySearchMarker} marker
+ * @param {Item} p
+ * @param {number} index
+ */
+const overwriteMarker = (marker, p, index) => {
+  marker.p.marker = false
+  marker.p = p
+  p.marker = true
+  marker.index = index
+  marker.timestamp = globalSearchMarkerTimestamp++
+}
+
+/**
+ * @param {Array<ArraySearchMarker>} searchMarker
+ * @param {Item} p
+ * @param {number} index
+ */
+const markPosition = (searchMarker, p, index) => {
+  if (searchMarker.length >= maxSearchMarker) {
+    // override oldest marker (we don't want to create more objects)
+    const marker = searchMarker.reduce((a, b) => a.timestamp < b.timestamp ? a : b)
+    overwriteMarker(marker, p, index)
+    return marker
+  } else {
+    // create new marker
+    const pm = new ArraySearchMarker(p, index)
+    searchMarker.push(pm)
+    return pm
+  }
+}
+
+/**
+ * Search marker help us to find positions in the associative array faster.
+ *
+ * They speed up the process of finding a position without much bookkeeping.
+ *
+ * A maximum of `maxSearchMarker` objects are created.
+ *
+ * This function always returns a refreshed marker (updated timestamp)
+ *
+ * @param {AbstractType<any>} yarray
+ * @param {number} index
+ */
+export const findMarker = (yarray, index) => {
+  if (yarray._start === null || index === 0 || yarray._searchMarker === null) {
+    return null
+  }
+  const marker = yarray._searchMarker.length === 0 ? null : yarray._searchMarker.reduce((a, b) => math.abs(index - a.index) < math.abs(index - b.index) ? a : b)
+  let p = yarray._start
+  let pindex = 0
+  if (marker !== null) {
+    p = marker.p
+    pindex = marker.index
+    refreshMarkerTimestamp(marker) // we used it, we might need to use it again
+  }
+  // iterate to right if possible
+  while (p.right !== null && pindex < index) {
+    if (!p.deleted && p.countable) {
+      if (index < pindex + p.length) {
+        break
+      }
+      pindex += p.length
+    }
+    p = p.right
+  }
+  // iterate to left if necessary (might be that pindex > index)
+  while (p.left !== null && pindex > index) {
+    p = p.left
+    if (!p.deleted && p.countable) {
+      pindex -= p.length
+    }
+  }
+  // we want to make sure that p can't be merged with left, because that would screw up everything
+  // in that cas just return what we have (it is most likely the best marker anyway)
+  // iterate to left until p can't be merged with left
+  while (p.left !== null && p.left.id.client === p.id.client && p.left.id.clock + p.left.length === p.id.clock) {
+    p = p.left
+    if (!p.deleted && p.countable) {
+      pindex -= p.length
+    }
+  }
+
+  // @todo remove!
+  // assure position
+  // {
+  //   let start = yarray._start
+  //   let pos = 0
+  //   while (start !== p) {
+  //     if (!start.deleted && start.countable) {
+  //       pos += start.length
+  //     }
+  //     start = /** @type {Item} */ (start.right)
+  //   }
+  //   if (pos !== pindex) {
+  //     debugger
+  //     throw new Error('Gotcha position fail!')
+  //   }
+  // }
+  // if (marker) {
+  //   if (window.lengthes == null) {
+  //     window.lengthes = []
+  //     window.getLengthes = () => window.lengthes.sort((a, b) => a - b)
+  //   }
+  //   window.lengthes.push(marker.index - pindex)
+  //   console.log('distance', marker.index - pindex, 'len', p && p.parent.length)
+  // }
+  if (marker !== null && math.abs(marker.index - pindex) < /** @type {YText|YArray<any>} */ (p.parent).length / maxSearchMarker) {
+    // adjust existing marker
+    overwriteMarker(marker, p, pindex)
+    return marker
+  } else {
+    // create new marker
+    return markPosition(yarray._searchMarker, p, pindex)
+  }
+}
+
+/**
+ * Update markers when a change happened.
+ *
+ * This should be called before doing a deletion!
+ *
+ * @param {Array<ArraySearchMarker>} searchMarker
+ * @param {number} index
+ * @param {number} len If insertion, len is positive. If deletion, len is negative.
+ */
+export const updateMarkerChanges = (searchMarker, index, len) => {
+  for (let i = searchMarker.length - 1; i >= 0; i--) {
+    const m = searchMarker[i]
+    if (len > 0) {
+      /**
+       * @type {Item|null}
+       */
+      let p = m.p
+      p.marker = false
+      // Ideally we just want to do a simple position comparison, but this will only work if
+      // search markers don't point to deleted items for formats.
+      // Iterate marker to prev undeleted countable position so we know what to do when updating a position
+      while (p && (p.deleted || !p.countable)) {
+        p = p.left
+        if (p && !p.deleted && p.countable) {
+          // adjust position. the loop should break now
+          m.index -= p.length
+        }
+      }
+      if (p === null || p.marker === true) {
+        // remove search marker if updated position is null or if position is already marked
+        searchMarker.splice(i, 1)
+        continue
+      }
+      m.p = p
+      p.marker = true
+    }
+    if (index < m.index || (len > 0 && index === m.index)) { // a simple index <= m.index check would actually suffice
+      m.index = math.max(index, m.index + len)
+    }
+  }
+}
+
+/**
+ * Accumulate all (list) children of a type and return them as an Array.
+ *
+ * @param {AbstractType<any>} t
+ * @return {Array<Item>}
+ */
+export const getTypeChildren = t => {
+  let s = t._start
+  const arr = []
+  while (s) {
+    arr.push(s)
+    s = s.right
+  }
+  return arr
+}
+
+/**
+ * Call event listeners with an event. This will also add an event to all
+ * parents (for `.observeDeep` handlers).
+ *
+ * @template EventType
+ * @param {AbstractType<EventType>} type
+ * @param {Transaction} transaction
+ * @param {EventType} event
+ */
+export const callTypeObservers = (type, transaction, event) => {
+  const changedType = type
+  const changedParentTypes = transaction.changedParentTypes
+  while (true) {
+    // @ts-ignore
+    map.setIfUndefined(changedParentTypes, type, () => []).push(event)
+    if (type._item === null) {
+      break
+    }
+    type = /** @type {AbstractType<any>} */ (type._item.parent)
+  }
+  callEventHandlerListeners(changedType._eH, event, transaction)
+}
+
+/**
+ * @template EventType
+ * Abstract Yjs Type class
+ */
+export class AbstractType {
+  constructor () {
+    /**
+     * @type {Item|null}
+     */
+    this._item = null
+    /**
+     * @type {Map<string,Item>}
+     */
+    this._map = new Map()
+    /**
+     * @type {Item|null}
+     */
+    this._start = null
+    /**
+     * @type {Doc|null}
+     */
+    this.doc = null
+    this._length = 0
+    /**
+     * Event handlers
+     * @type {EventHandler<EventType,Transaction>}
+     */
+    this._eH = createEventHandler()
+    /**
+     * Deep event handlers
+     * @type {EventHandler<Array<YEvent>,Transaction>}
+     */
+    this._dEH = createEventHandler()
+    /**
+     * @type {null | Array<ArraySearchMarker>}
+     */
+    this._searchMarker = null
+  }
+
+  /**
+   * @return {AbstractType<any>|null}
+   */
+  get parent () {
+    return this._item ? /** @type {AbstractType<any>} */ (this._item.parent) : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item|null} item
+   */
+  _integrate (y, item) {
+    this.doc = y
+    this._item = item
+  }
+
+  /**
+   * @return {AbstractType<EventType>}
+   */
+  _copy () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {AbstractType<EventType>}
+   */
+  clone () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) { }
+
+  /**
+   * The first non-deleted item
+   */
+  get _first () {
+    let n = this._start
+    while (n !== null && n.deleted) {
+      n = n.right
+    }
+    return n
+  }
+
+  /**
+   * Creates YEvent and calls all type observers.
+   * Must be implemented by each type.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    if (!transaction.local && this._searchMarker) {
+      this._searchMarker.length = 0
+    }
+  }
+
+  /**
+   * Observe all events that are created on this type.
+   *
+   * @param {function(EventType, Transaction):void} f Observer function
+   */
+  observe (f) {
+    addEventHandlerListener(this._eH, f)
+  }
+
+  /**
+   * Observe all events that are created by this type and its children.
+   *
+   * @param {function(Array<YEvent>,Transaction):void} f Observer function
+   */
+  observeDeep (f) {
+    addEventHandlerListener(this._dEH, f)
+  }
+
+  /**
+   * Unregister an observer function.
+   *
+   * @param {function(EventType,Transaction):void} f Observer function
+   */
+  unobserve (f) {
+    removeEventHandlerListener(this._eH, f)
+  }
+
+  /**
+   * Unregister an observer function.
+   *
+   * @param {function(Array<YEvent>,Transaction):void} f Observer function
+   */
+  unobserveDeep (f) {
+    removeEventHandlerListener(this._dEH, f)
+  }
+
+  /**
+   * @abstract
+   * @return {any}
+   */
+  toJSON () {}
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} start
+ * @param {number} end
+ * @return {Array<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListSlice = (type, start, end) => {
+  if (start < 0) {
+    start = type._length + start
+  }
+  if (end < 0) {
+    end = type._length + end
+  }
+  let len = end - start
+  const cs = []
+  let n = type._start
+  while (n !== null && len > 0) {
+    if (n.countable && !n.deleted) {
+      const c = n.content.getContent()
+      if (c.length <= start) {
+        start -= c.length
+      } else {
+        for (let i = start; i < c.length && len > 0; i++) {
+          cs.push(c[i])
+          len--
+        }
+        start = 0
+      }
+    }
+    n = n.right
+  }
+  return cs
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @return {Array<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListToArray = type => {
+  const cs = []
+  let n = type._start
+  while (n !== null) {
+    if (n.countable && !n.deleted) {
+      const c = n.content.getContent()
+      for (let i = 0; i < c.length; i++) {
+        cs.push(c[i])
+      }
+    }
+    n = n.right
+  }
+  return cs
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {Snapshot} snapshot
+ * @return {Array<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListToArraySnapshot = (type, snapshot) => {
+  const cs = []
+  let n = type._start
+  while (n !== null) {
+    if (n.countable && isVisible(n, snapshot)) {
+      const c = n.content.getContent()
+      for (let i = 0; i < c.length; i++) {
+        cs.push(c[i])
+      }
+    }
+    n = n.right
+  }
+  return cs
+}
+
+/**
+ * Executes a provided function on once on overy element of this YArray.
+ *
+ * @param {AbstractType<any>} type
+ * @param {function(any,number,any):void} f A function to execute on every element of this YArray.
+ *
+ * @private
+ * @function
+ */
+export const typeListForEach = (type, f) => {
+  let index = 0
+  let n = type._start
+  while (n !== null) {
+    if (n.countable && !n.deleted) {
+      const c = n.content.getContent()
+      for (let i = 0; i < c.length; i++) {
+        f(c[i], index++, type)
+      }
+    }
+    n = n.right
+  }
+}
+
+/**
+ * @template C,R
+ * @param {AbstractType<any>} type
+ * @param {function(C,number,AbstractType<any>):R} f
+ * @return {Array<R>}
+ *
+ * @private
+ * @function
+ */
+export const typeListMap = (type, f) => {
+  /**
+   * @type {Array<any>}
+   */
+  const result = []
+  typeListForEach(type, (c, i) => {
+    result.push(f(c, i, type))
+  })
+  return result
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @return {IterableIterator<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListCreateIterator = type => {
+  let n = type._start
+  /**
+   * @type {Array<any>|null}
+   */
+  let currentContent = null
+  let currentContentIndex = 0
+  return {
+    [Symbol.iterator] () {
+      return this
+    },
+    next: () => {
+      // find some content
+      if (currentContent === null) {
+        while (n !== null && n.deleted) {
+          n = n.right
+        }
+        // check if we reached the end, no need to check currentContent, because it does not exist
+        if (n === null) {
+          return {
+            done: true,
+            value: undefined
+          }
+        }
+        // we found n, so we can set currentContent
+        currentContent = n.content.getContent()
+        currentContentIndex = 0
+        n = n.right // we used the content of n, now iterate to next
+      }
+      const value = currentContent[currentContentIndex++]
+      // check if we need to empty currentContent
+      if (currentContent.length <= currentContentIndex) {
+        currentContent = null
+      }
+      return {
+        done: false,
+        value
+      }
+    }
+  }
+}
+
+/**
+ * Executes a provided function on once on overy element of this YArray.
+ * Operates on a snapshotted state of the document.
+ *
+ * @param {AbstractType<any>} type
+ * @param {function(any,number,AbstractType<any>):void} f A function to execute on every element of this YArray.
+ * @param {Snapshot} snapshot
+ *
+ * @private
+ * @function
+ */
+export const typeListForEachSnapshot = (type, f, snapshot) => {
+  let index = 0
+  let n = type._start
+  while (n !== null) {
+    if (n.countable && isVisible(n, snapshot)) {
+      const c = n.content.getContent()
+      for (let i = 0; i < c.length; i++) {
+        f(c[i], index++, type)
+      }
+    }
+    n = n.right
+  }
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} index
+ * @return {any}
+ *
+ * @private
+ * @function
+ */
+export const typeListGet = (type, index) => {
+  const marker = findMarker(type, index)
+  let n = type._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+  }
+  for (; n !== null; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index < n.length) {
+        return n.content.getContent()[index]
+      }
+      index -= n.length
+    }
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item?} referenceItem
+ * @param {Array<Object<string,any>|Array<any>|boolean|number|null|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenericsAfter = (transaction, parent, referenceItem, content) => {
+  let left = referenceItem
+  const doc = transaction.doc
+  const ownClientId = doc.clientID
+  const store = doc.store
+  const right = referenceItem === null ? parent._start : referenceItem.right
+  /**
+   * @type {Array<Object|Array<any>|number|null>}
+   */
+  let jsonContent = []
+  const packJsonContent = () => {
+    if (jsonContent.length > 0) {
+      left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentAny(jsonContent))
+      left.integrate(transaction, 0)
+      jsonContent = []
+    }
+  }
+  content.forEach(c => {
+    if (c === null) {
+      jsonContent.push(c)
+    } else {
+      switch (c.constructor) {
+        case Number:
+        case Object:
+        case Boolean:
+        case Array:
+        case String:
+          jsonContent.push(c)
+          break
+        default:
+          packJsonContent()
+          switch (c.constructor) {
+            case Uint8Array:
+            case ArrayBuffer:
+              left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentBinary(new Uint8Array(/** @type {Uint8Array} */ (c))))
+              left.integrate(transaction, 0)
+              break
+            case Doc:
+              left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentDoc(/** @type {Doc} */ (c)))
+              left.integrate(transaction, 0)
+              break
+            default:
+              if (c instanceof AbstractType) {
+                left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentType(c))
+                left.integrate(transaction, 0)
+              } else {
+                throw new Error('Unexpected content type in insert operation')
+              }
+          }
+      }
+    }
+  })
+  packJsonContent()
+}
+
+const lengthExceeded = error.create('Length exceeded!')
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @param {Array<Object<string,any>|Array<any>|number|null|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenerics = (transaction, parent, index, content) => {
+  if (index > parent._length) {
+    throw lengthExceeded
+  }
+  if (index === 0) {
+    if (parent._searchMarker) {
+      updateMarkerChanges(parent._searchMarker, index, content.length)
+    }
+    return typeListInsertGenericsAfter(transaction, parent, null, content)
+  }
+  const startIndex = index
+  const marker = findMarker(parent, index)
+  let n = parent._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+    // we need to iterate one to the left so that the algorithm works
+    if (index === 0) {
+      // @todo refactor this as it actually doesn't consider formats
+      n = n.prev // important! get the left undeleted item so that we can actually decrease index
+      index += (n && n.countable && !n.deleted) ? n.length : 0
+    }
+  }
+  for (; n !== null; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index <= n.length) {
+        if (index < n.length) {
+          // insert in-between
+          getItemCleanStart(transaction, createID(n.id.client, n.id.clock + index))
+        }
+        break
+      }
+      index -= n.length
+    }
+  }
+  if (parent._searchMarker) {
+    updateMarkerChanges(parent._searchMarker, startIndex, content.length)
+  }
+  return typeListInsertGenericsAfter(transaction, parent, n, content)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @param {number} length
+ *
+ * @private
+ * @function
+ */
+export const typeListDelete = (transaction, parent, index, length) => {
+  if (length === 0) { return }
+  const startIndex = index
+  const startLength = length
+  const marker = findMarker(parent, index)
+  let n = parent._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+  }
+  // compute the first item to be deleted
+  for (; n !== null && index > 0; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index < n.length) {
+        getItemCleanStart(transaction, createID(n.id.client, n.id.clock + index))
+      }
+      index -= n.length
+    }
+  }
+  // delete all items until done
+  while (length > 0 && n !== null) {
+    if (!n.deleted) {
+      if (length < n.length) {
+        getItemCleanStart(transaction, createID(n.id.client, n.id.clock + length))
+      }
+      n.delete(transaction)
+      length -= n.length
+    }
+    n = n.right
+  }
+  if (length > 0) {
+    throw lengthExceeded
+  }
+  if (parent._searchMarker) {
+    updateMarkerChanges(parent._searchMarker, startIndex, -startLength + length /* in case we remove the above exception */)
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ *
+ * @private
+ * @function
+ */
+export const typeMapDelete = (transaction, parent, key) => {
+  const c = parent._map.get(key)
+  if (c !== undefined) {
+    c.delete(transaction)
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @param {Object|number|null|Array<any>|string|Uint8Array|AbstractType<any>} value
+ *
+ * @private
+ * @function
+ */
+export const typeMapSet = (transaction, parent, key, value) => {
+  const left = parent._map.get(key) || null
+  const doc = transaction.doc
+  const ownClientId = doc.clientID
+  let content
+  if (value == null) {
+    content = new ContentAny([value])
+  } else {
+    switch (value.constructor) {
+      case Number:
+      case Object:
+      case Boolean:
+      case Array:
+      case String:
+        content = new ContentAny([value])
+        break
+      case Uint8Array:
+        content = new ContentBinary(/** @type {Uint8Array} */ (value))
+        break
+      case Doc:
+        content = new ContentDoc(/** @type {Doc} */ (value))
+        break
+      default:
+        if (value instanceof AbstractType) {
+          content = new ContentType(value)
+        } else {
+          throw new Error('Unexpected content type')
+        }
+    }
+  }
+  new Item(createID(ownClientId, getState(doc.store, ownClientId)), left, left && left.lastId, null, null, parent, key, content).integrate(transaction, 0)
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @return {Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGet = (parent, key) => {
+  const val = parent._map.get(key)
+  return val !== undefined && !val.deleted ? val.content.getContent()[val.length - 1] : undefined
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @return {Object<string,Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined>}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetAll = (parent) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const res = {}
+  parent._map.forEach((value, key) => {
+    if (!value.deleted) {
+      res[key] = value.content.getContent()[value.length - 1]
+    }
+  })
+  return res
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @return {boolean}
+ *
+ * @private
+ * @function
+ */
+export const typeMapHas = (parent, key) => {
+  const val = parent._map.get(key)
+  return val !== undefined && !val.deleted
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @param {Snapshot} snapshot
+ * @return {Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetSnapshot = (parent, key, snapshot) => {
+  let v = parent._map.get(key) || null
+  while (v !== null && (!snapshot.sv.has(v.id.client) || v.id.clock >= (snapshot.sv.get(v.id.client) || 0))) {
+    v = v.left
+  }
+  return v !== null && isVisible(v, snapshot) ? v.content.getContent()[v.length - 1] : undefined
+}
+
+/**
+ * @param {Map<string,Item>} map
+ * @return {IterableIterator<Array<any>>}
+ *
+ * @private
+ * @function
+ */
+export const createMapIterator = map => iterator.iteratorFilter(map.entries(), /** @param {any} entry */ entry => !entry[1].deleted)
--- a/src/types/YArray.js
+++ b/src/types/YArray.js
@@ -0,0 +1,257 @@
+/**
+ * @module YArray
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeListGet,
+  typeListToArray,
+  typeListForEach,
+  typeListCreateIterator,
+  typeListInsertGenerics,
+  typeListDelete,
+  typeListMap,
+  YArrayRefID,
+  callTypeObservers,
+  transact,
+  ArraySearchMarker, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+import { typeListSlice } from './AbstractType.js'
+
+/**
+ * Event that describes the changes on a YArray
+ * @template T
+ */
+export class YArrayEvent extends YEvent {
+  /**
+   * @param {YArray<T>} yarray The changed type
+   * @param {Transaction} transaction The transaction object
+   */
+  constructor (yarray, transaction) {
+    super(yarray, transaction)
+    this._transaction = transaction
+  }
+}
+
+/**
+ * A shared Array implementation.
+ * @template T
+ * @extends AbstractType<YArrayEvent<T>>
+ * @implements {Iterable<T>}
+ */
+export class YArray extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Array<any>?}
+     * @private
+     */
+    this._prelimContent = []
+    /**
+     * @type {Array<ArraySearchMarker>}
+     */
+    this._searchMarker = []
+  }
+
+  /**
+   * Construct a new YArray containing the specified items.
+   * @template T
+   * @param {Array<T>} items
+   * @return {YArray<T>}
+   */
+  static from (items) {
+    const a = new YArray()
+    a.push(items)
+    return a
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    this.insert(0, /** @type {Array<any>} */ (this._prelimContent))
+    this._prelimContent = null
+  }
+
+  _copy () {
+    return new YArray()
+  }
+
+  /**
+   * @return {YArray<T>}
+   */
+  clone () {
+    const arr = new YArray()
+    arr.insert(0, this.toArray().map(el =>
+      el instanceof AbstractType ? el.clone() : el
+    ))
+    return arr
+  }
+
+  get length () {
+    return this._prelimContent === null ? this._length : this._prelimContent.length
+  }
+
+  /**
+   * Creates YArrayEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    super._callObserver(transaction, parentSubs)
+    callTypeObservers(this, transaction, new YArrayEvent(this, transaction))
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * Important: This function expects an array of content. Not just a content
+   * object. The reason for this "weirdness" is that inserting several elements
+   * is very efficient when it is done as a single operation.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  yarray.insert(0, ['a'])
+   *  // Insert numbers 1, 2 at position 1
+   *  yarray.insert(1, [1, 2])
+   *
+   * @param {number} index The index to insert content at.
+   * @param {Array<T>} content The array of content
+   */
+  insert (index, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListInsertGenerics(transaction, this, index, content)
+      })
+    } else {
+      /** @type {Array<any>} */ (this._prelimContent).splice(index, 0, ...content)
+    }
+  }
+
+  /**
+   * Appends content to this YArray.
+   *
+   * @param {Array<T>} content Array of content to append.
+   */
+  push (content) {
+    this.insert(this.length, content)
+  }
+
+  /**
+   * Preppends content to this YArray.
+   *
+   * @param {Array<T>} content Array of content to preppend.
+   */
+  unshift (content) {
+    this.insert(0, content)
+  }
+
+  /**
+   * Deletes elements starting from an index.
+   *
+   * @param {number} index Index at which to start deleting elements
+   * @param {number} length The number of elements to remove. Defaults to 1.
+   */
+  delete (index, length = 1) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListDelete(transaction, this, index, length)
+      })
+    } else {
+      /** @type {Array<any>} */ (this._prelimContent).splice(index, length)
+    }
+  }
+
+  /**
+   * Returns the i-th element from a YArray.
+   *
+   * @param {number} index The index of the element to return from the YArray
+   * @return {T}
+   */
+  get (index) {
+    return typeListGet(this, index)
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @return {Array<T>}
+   */
+  toArray () {
+    return typeListToArray(this)
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @param {number} [start]
+   * @param {number} [end]
+   * @return {Array<T>}
+   */
+  slice (start = 0, end = this.length) {
+    return typeListSlice(this, start, end)
+  }
+
+  /**
+   * Transforms this Shared Type to a JSON object.
+   *
+   * @return {Array<any>}
+   */
+  toJSON () {
+    return this.map(c => c instanceof AbstractType ? c.toJSON() : c)
+  }
+
+  /**
+   * Returns an Array with the result of calling a provided function on every
+   * element of this YArray.
+   *
+   * @template M
+   * @param {function(T,number,YArray<T>):M} f Function that produces an element of the new Array
+   * @return {Array<M>} A new array with each element being the result of the
+   *                 callback function
+   */
+  map (f) {
+    return typeListMap(this, /** @type {any} */ (f))
+  }
+
+  /**
+   * Executes a provided function on once on overy element of this YArray.
+   *
+   * @param {function(T,number,YArray<T>):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    typeListForEach(this, f)
+  }
+
+  /**
+   * @return {IterableIterator<T>}
+   */
+  [Symbol.iterator] () {
+    return typeListCreateIterator(this)
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YArrayRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ *
+ * @private
+ * @function
+ */
+export const readYArray = decoder => new YArray()
--- a/src/types/YMap.js
+++ b/src/types/YMap.js
@@ -0,0 +1,269 @@
+
+/**
+ * @module YMap
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeMapDelete,
+  typeMapSet,
+  typeMapGet,
+  typeMapHas,
+  createMapIterator,
+  YMapRefID,
+  callTypeObservers,
+  transact,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as iterator from 'lib0/iterator'
+
+/**
+ * @template T
+ * Event that describes the changes on a YMap.
+ */
+export class YMapEvent extends YEvent {
+  /**
+   * @param {YMap<T>} ymap The YArray that changed.
+   * @param {Transaction} transaction
+   * @param {Set<any>} subs The keys that changed.
+   */
+  constructor (ymap, transaction, subs) {
+    super(ymap, transaction)
+    this.keysChanged = subs
+  }
+}
+
+/**
+ * @template MapType
+ * A shared Map implementation.
+ *
+ * @extends AbstractType<YMapEvent<MapType>>
+ * @implements {Iterable<MapType>}
+ */
+export class YMap extends AbstractType {
+  /**
+   *
+   * @param {Iterable<readonly [string, any]>=} entries - an optional iterable to initialize the YMap
+   */
+  constructor (entries) {
+    super()
+    /**
+     * @type {Map<string,any>?}
+     * @private
+     */
+    this._prelimContent = null
+
+    if (entries === undefined) {
+      this._prelimContent = new Map()
+    } else {
+      this._prelimContent = new Map(entries)
+    }
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    ;/** @type {Map<string, any>} */ (this._prelimContent).forEach((value, key) => {
+      this.set(key, value)
+    })
+    this._prelimContent = null
+  }
+
+  _copy () {
+    return new YMap()
+  }
+
+  /**
+   * @return {YMap<MapType>}
+   */
+  clone () {
+    const map = new YMap()
+    this.forEach((value, key) => {
+      map.set(key, value instanceof AbstractType ? value.clone() : value)
+    })
+    return map
+  }
+
+  /**
+   * Creates YMapEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    callTypeObservers(this, transaction, new YMapEvent(this, transaction, parentSubs))
+  }
+
+  /**
+   * Transforms this Shared Type to a JSON object.
+   *
+   * @return {Object<string,any>}
+   */
+  toJSON () {
+    /**
+     * @type {Object<string,MapType>}
+     */
+    const map = {}
+    this._map.forEach((item, key) => {
+      if (!item.deleted) {
+        const v = item.content.getContent()[item.length - 1]
+        map[key] = v instanceof AbstractType ? v.toJSON() : v
+      }
+    })
+    return map
+  }
+
+  /**
+   * Returns the size of the YMap (count of key/value pairs)
+   *
+   * @return {number}
+   */
+  get size () {
+    return [...createMapIterator(this._map)].length
+  }
+
+  /**
+   * Returns the keys for each element in the YMap Type.
+   *
+   * @return {IterableIterator<string>}
+   */
+  keys () {
+    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => v[0])
+  }
+
+  /**
+   * Returns the values for each element in the YMap Type.
+   *
+   * @return {IterableIterator<any>}
+   */
+  values () {
+    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => v[1].content.getContent()[v[1].length - 1])
+  }
+
+  /**
+   * Returns an Iterator of [key, value] pairs
+   *
+   * @return {IterableIterator<any>}
+   */
+  entries () {
+    return iterator.iteratorMap(createMapIterator(this._map), /** @param {any} v */ v => [v[0], v[1].content.getContent()[v[1].length - 1]])
+  }
+
+  /**
+   * Executes a provided function on once on every key-value pair.
+   *
+   * @param {function(MapType,string,YMap<MapType>):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    /**
+     * @type {Object<string,MapType>}
+     */
+    const map = {}
+    this._map.forEach((item, key) => {
+      if (!item.deleted) {
+        f(item.content.getContent()[item.length - 1], key, this)
+      }
+    })
+    return map
+  }
+
+  /**
+   * @return {IterableIterator<MapType>}
+   */
+  [Symbol.iterator] () {
+    return this.entries()
+  }
+
+  /**
+   * Remove a specified element from this YMap.
+   *
+   * @param {string} key The key of the element to remove.
+   */
+  delete (key) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapDelete(transaction, this, key)
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).delete(key)
+    }
+  }
+
+  /**
+   * Adds or updates an element with a specified key and value.
+   *
+   * @param {string} key The key of the element to add to this YMap
+   * @param {MapType} value The value of the element to add
+   */
+  set (key, value) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapSet(transaction, this, key, value)
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).set(key, value)
+    }
+    return value
+  }
+
+  /**
+   * Returns a specified element from this YMap.
+   *
+   * @param {string} key
+   * @return {MapType|undefined}
+   */
+  get (key) {
+    return /** @type {any} */ (typeMapGet(this, key))
+  }
+
+  /**
+   * Returns a boolean indicating whether the specified key exists or not.
+   *
+   * @param {string} key The key to test.
+   * @return {boolean}
+   */
+  has (key) {
+    return typeMapHas(this, key)
+  }
+
+  /**
+   * Removes all elements from this YMap.
+   */
+  clear () {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        this.forEach(function (value, key, map) {
+          typeMapDelete(transaction, map, key)
+        })
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).clear()
+    }
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YMapRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ *
+ * @private
+ * @function
+ */
+export const readYMap = decoder => new YMap()
--- a/src/types/YText.js
+++ b/src/types/YText.js
--- a/src/types/YXmlElement.js
+++ b/src/types/YXmlElement.js
@@ -0,0 +1,238 @@
+
+import {
+  YXmlFragment,
+  transact,
+  typeMapDelete,
+  typeMapHas,
+  typeMapSet,
+  typeMapGet,
+  typeMapGetAll,
+  typeListForEach,
+  YXmlElementRefID,
+  YXmlText, ContentType, AbstractType, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Snapshot, Doc, Item // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * An YXmlElement imitates the behavior of a
+ * {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}.
+ *
+ * * An YXmlElement has attributes (key value pairs)
+ * * An YXmlElement has childElements that must inherit from YXmlElement
+ */
+export class YXmlElement extends YXmlFragment {
+  constructor (nodeName = 'UNDEFINED') {
+    super()
+    this.nodeName = nodeName
+    /**
+     * @type {Map<string, any>|null}
+     */
+    this._prelimAttrs = new Map()
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get nextSibling () {
+    const n = this._item ? this._item.next : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get prevSibling () {
+    const n = this._item ? this._item.prev : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    ;(/** @type {Map<string, any>} */ (this._prelimAttrs)).forEach((value, key) => {
+      this.setAttribute(key, value)
+    })
+    this._prelimAttrs = null
+  }
+
+  /**
+   * Creates an Item with the same effect as this Item (without position effect)
+   *
+   * @return {YXmlElement}
+   */
+  _copy () {
+    return new YXmlElement(this.nodeName)
+  }
+
+  /**
+   * @return {YXmlElement}
+   */
+  clone () {
+    const el = new YXmlElement(this.nodeName)
+    const attrs = this.getAttributes()
+    for (const key in attrs) {
+      el.setAttribute(key, attrs[key])
+    }
+    // @ts-ignore
+    el.insert(0, this.toArray().map(item => item instanceof AbstractType ? item.clone() : item))
+    return el
+  }
+
+  /**
+   * Returns the XML serialization of this YXmlElement.
+   * The attributes are ordered by attribute-name, so you can easily use this
+   * method to compare YXmlElements
+   *
+   * @return {string} The string representation of this type.
+   *
+   * @public
+   */
+  toString () {
+    const attrs = this.getAttributes()
+    const stringBuilder = []
+    const keys = []
+    for (const key in attrs) {
+      keys.push(key)
+    }
+    keys.sort()
+    const keysLen = keys.length
+    for (let i = 0; i < keysLen; i++) {
+      const key = keys[i]
+      stringBuilder.push(key + '="' + attrs[key] + '"')
+    }
+    const nodeName = this.nodeName.toLocaleLowerCase()
+    const attrsString = stringBuilder.length > 0 ? ' ' + stringBuilder.join(' ') : ''
+    return `<${nodeName}${attrsString}>${super.toString()}</${nodeName}>`
+  }
+
+  /**
+   * Removes an attribute from this YXmlElement.
+   *
+   * @param {String} attributeName The attribute name that is to be removed.
+   *
+   * @public
+   */
+  removeAttribute (attributeName) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapDelete(transaction, this, attributeName)
+      })
+    } else {
+      /** @type {Map<string,any>} */ (this._prelimAttrs).delete(attributeName)
+    }
+  }
+
+  /**
+   * Sets or updates an attribute.
+   *
+   * @param {String} attributeName The attribute name that is to be set.
+   * @param {String} attributeValue The attribute value that is to be set.
+   *
+   * @public
+   */
+  setAttribute (attributeName, attributeValue) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapSet(transaction, this, attributeName, attributeValue)
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimAttrs).set(attributeName, attributeValue)
+    }
+  }
+
+  /**
+   * Returns an attribute value that belongs to the attribute name.
+   *
+   * @param {String} attributeName The attribute name that identifies the
+   *                               queried value.
+   * @return {String} The queried attribute value.
+   *
+   * @public
+   */
+  getAttribute (attributeName) {
+    return /** @type {any} */ (typeMapGet(this, attributeName))
+  }
+
+  /**
+   * Returns whether an attribute exists
+   *
+   * @param {String} attributeName The attribute name to check for existence.
+   * @return {boolean} whether the attribute exists.
+   *
+   * @public
+   */
+  hasAttribute (attributeName) {
+    return /** @type {any} */ (typeMapHas(this, attributeName))
+  }
+
+  /**
+   * Returns all attribute name/value pairs in a JSON Object.
+   *
+   * @param {Snapshot} [snapshot]
+   * @return {Object<string, any>} A JSON Object that describes the attributes.
+   *
+   * @public
+   */
+  getAttributes (snapshot) {
+    return typeMapGetAll(this)
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlElement.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object<string, any>} [hooks={}] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type.
+   * @return {Node} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks = {}, binding) {
+    const dom = _document.createElement(this.nodeName)
+    const attrs = this.getAttributes()
+    for (const key in attrs) {
+      dom.setAttribute(key, attrs[key])
+    }
+    typeListForEach(this, yxml => {
+      dom.appendChild(yxml.toDOM(_document, hooks, binding))
+    })
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlElementRefID)
+    encoder.writeKey(this.nodeName)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlElement}
+ *
+ * @function
+ */
+export const readYXmlElement = decoder => new YXmlElement(decoder.readKey())
--- a/src/types/YXmlEvent.js
+++ b/src/types/YXmlEvent.js
@@ -0,0 +1,39 @@
+
+import {
+  YEvent,
+  YXmlText, YXmlElement, YXmlFragment, Transaction // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * An Event that describes changes on a YXml Element or Yxml Fragment
+ */
+export class YXmlEvent extends YEvent {
+  /**
+   * @param {YXmlElement|YXmlText|YXmlFragment} target The target on which the event is created.
+   * @param {Set<string|null>} subs The set of changed attributes. `null` is included if the
+   *                   child list changed.
+   * @param {Transaction} transaction The transaction instance with wich the
+   *                                  change was created.
+   */
+  constructor (target, subs, transaction) {
+    super(target, transaction)
+    /**
+     * Whether the children changed.
+     * @type {Boolean}
+     * @private
+     */
+    this.childListChanged = false
+    /**
+     * Set of all changed attributes.
+     * @type {Set<string>}
+     */
+    this.attributesChanged = new Set()
+    subs.forEach((sub) => {
+      if (sub === null) {
+        this.childListChanged = true
+      } else {
+        this.attributesChanged.add(sub)
+      }
+    })
+  }
+}
--- a/src/types/YXmlFragment.js
+++ b/src/types/YXmlFragment.js
@@ -0,0 +1,427 @@
+/**
+ * @module YXml
+ */
+
+import {
+  YXmlEvent,
+  YXmlElement,
+  AbstractType,
+  typeListMap,
+  typeListForEach,
+  typeListInsertGenerics,
+  typeListInsertGenericsAfter,
+  typeListDelete,
+  typeListToArray,
+  YXmlFragmentRefID,
+  callTypeObservers,
+  transact,
+  typeListGet,
+  typeListSlice,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, ContentType, Transaction, Item, YXmlText, YXmlHook, Snapshot // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * Define the elements to which a set of CSS queries apply.
+ * {@link https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors|CSS_Selectors}
+ *
+ * @example
+ *   query = '.classSelector'
+ *   query = 'nodeSelector'
+ *   query = '#idSelector'
+ *
+ * @typedef {string} CSS_Selector
+ */
+
+/**
+ * Dom filter function.
+ *
+ * @callback domFilter
+ * @param {string} nodeName The nodeName of the element
+ * @param {Map} attributes The map of attributes.
+ * @return {boolean} Whether to include the Dom node in the YXmlElement.
+ */
+
+/**
+ * Represents a subset of the nodes of a YXmlElement / YXmlFragment and a
+ * position within them.
+ *
+ * Can be created with {@link YXmlFragment#createTreeWalker}
+ *
+ * @public
+ * @implements {Iterable<YXmlElement|YXmlText|YXmlElement|YXmlHook>}
+ */
+export class YXmlTreeWalker {
+  /**
+   * @param {YXmlFragment | YXmlElement} root
+   * @param {function(AbstractType<any>):boolean} [f]
+   */
+  constructor (root, f = () => true) {
+    this._filter = f
+    this._root = root
+    /**
+     * @type {Item}
+     */
+    this._currentNode = /** @type {Item} */ (root._start)
+    this._firstCall = true
+  }
+
+  [Symbol.iterator] () {
+    return this
+  }
+
+  /**
+   * Get the next node.
+   *
+   * @return {IteratorResult<YXmlElement|YXmlText|YXmlHook>} The next node.
+   *
+   * @public
+   */
+  next () {
+    /**
+     * @type {Item|null}
+     */
+    let n = this._currentNode
+    let type = n && n.content && /** @type {any} */ (n.content).type
+    if (n !== null && (!this._firstCall || n.deleted || !this._filter(type))) { // if first call, we check if we can use the first item
+      do {
+        type = /** @type {any} */ (n.content).type
+        if (!n.deleted && (type.constructor === YXmlElement || type.constructor === YXmlFragment) && type._start !== null) {
+          // walk down in the tree
+          n = type._start
+        } else {
+          // walk right or up in the tree
+          while (n !== null) {
+            if (n.right !== null) {
+              n = n.right
+              break
+            } else if (n.parent === this._root) {
+              n = null
+            } else {
+              n = /** @type {AbstractType<any>} */ (n.parent)._item
+            }
+          }
+        }
+      } while (n !== null && (n.deleted || !this._filter(/** @type {ContentType} */ (n.content).type)))
+    }
+    this._firstCall = false
+    if (n === null) {
+      // @ts-ignore
+      return { value: undefined, done: true }
+    }
+    this._currentNode = n
+    return { value: /** @type {any} */ (n.content).type, done: false }
+  }
+}
+
+/**
+ * Represents a list of {@link YXmlElement}.and {@link YXmlText} types.
+ * A YxmlFragment is similar to a {@link YXmlElement}, but it does not have a
+ * nodeName and it does not have attributes. Though it can be bound to a DOM
+ * element - in this case the attributes and the nodeName are not shared.
+ *
+ * @public
+ * @extends AbstractType<YXmlEvent>
+ */
+export class YXmlFragment extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Array<any>|null}
+     */
+    this._prelimContent = []
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get firstChild () {
+    const first = this._first
+    return first ? first.content.getContent()[0] : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    this.insert(0, /** @type {Array<any>} */ (this._prelimContent))
+    this._prelimContent = null
+  }
+
+  _copy () {
+    return new YXmlFragment()
+  }
+
+  /**
+   * @return {YXmlFragment}
+   */
+  clone () {
+    const el = new YXmlFragment()
+    // @ts-ignore
+    el.insert(0, this.toArray().map(item => item instanceof AbstractType ? item.clone() : item))
+    return el
+  }
+
+  get length () {
+    return this._prelimContent === null ? this._length : this._prelimContent.length
+  }
+
+  /**
+   * Create a subtree of childNodes.
+   *
+   * @example
+   * const walker = elem.createTreeWalker(dom => dom.nodeName === 'div')
+   * for (let node in walker) {
+   *   // `node` is a div node
+   *   nop(node)
+   * }
+   *
+   * @param {function(AbstractType<any>):boolean} filter Function that is called on each child element and
+   *                          returns a Boolean indicating whether the child
+   *                          is to be included in the subtree.
+   * @return {YXmlTreeWalker} A subtree and a position within it.
+   *
+   * @public
+   */
+  createTreeWalker (filter) {
+    return new YXmlTreeWalker(this, filter)
+  }
+
+  /**
+   * Returns the first YXmlElement that matches the query.
+   * Similar to DOM's {@link querySelector}.
+   *
+   * Query support:
+   *   - tagname
+   * TODO:
+   *   - id
+   *   - attribute
+   *
+   * @param {CSS_Selector} query The query on the children.
+   * @return {YXmlElement|YXmlText|YXmlHook|null} The first element that matches the query or null.
+   *
+   * @public
+   */
+  querySelector (query) {
+    query = query.toUpperCase()
+    // @ts-ignore
+    const iterator = new YXmlTreeWalker(this, element => element.nodeName && element.nodeName.toUpperCase() === query)
+    const next = iterator.next()
+    if (next.done) {
+      return null
+    } else {
+      return next.value
+    }
+  }
+
+  /**
+   * Returns all YXmlElements that match the query.
+   * Similar to Dom's {@link querySelectorAll}.
+   *
+   * @todo Does not yet support all queries. Currently only query by tagName.
+   *
+   * @param {CSS_Selector} query The query on the children
+   * @return {Array<YXmlElement|YXmlText|YXmlHook|null>} The elements that match this query.
+   *
+   * @public
+   */
+  querySelectorAll (query) {
+    query = query.toUpperCase()
+    // @ts-ignore
+    return Array.from(new YXmlTreeWalker(this, element => element.nodeName && element.nodeName.toUpperCase() === query))
+  }
+
+  /**
+   * Creates YXmlEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    callTypeObservers(this, transaction, new YXmlEvent(this, parentSubs, transaction))
+  }
+
+  /**
+   * Get the string representation of all the children of this YXmlFragment.
+   *
+   * @return {string} The string representation of all children.
+   */
+  toString () {
+    return typeListMap(this, xml => xml.toString()).join('')
+  }
+
+  /**
+   * @return {string}
+   */
+  toJSON () {
+    return this.toString()
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlElement.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object<string, any>} [hooks={}] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type.
+   * @return {Node} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks = {}, binding) {
+    const fragment = _document.createDocumentFragment()
+    if (binding !== undefined) {
+      binding._createAssociation(fragment, this)
+    }
+    typeListForEach(this, xmlType => {
+      fragment.insertBefore(xmlType.toDOM(_document, hooks, binding), null)
+    })
+    return fragment
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  xml.insert(0, [new Y.XmlText('text')])
+   *
+   * @param {number} index The index to insert content at
+   * @param {Array<YXmlElement|YXmlText>} content The array of content
+   */
+  insert (index, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListInsertGenerics(transaction, this, index, content)
+      })
+    } else {
+      // @ts-ignore _prelimContent is defined because this is not yet integrated
+      this._prelimContent.splice(index, 0, ...content)
+    }
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  xml.insert(0, [new Y.XmlText('text')])
+   *
+   * @param {null|Item|YXmlElement|YXmlText} ref The index to insert content at
+   * @param {Array<YXmlElement|YXmlText>} content The array of content
+   */
+  insertAfter (ref, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        const refItem = (ref && ref instanceof AbstractType) ? ref._item : ref
+        typeListInsertGenericsAfter(transaction, this, refItem, content)
+      })
+    } else {
+      const pc = /** @type {Array<any>} */ (this._prelimContent)
+      const index = ref === null ? 0 : pc.findIndex(el => el === ref) + 1
+      if (index === 0 && ref !== null) {
+        throw error.create('Reference item not found')
+      }
+      pc.splice(index, 0, ...content)
+    }
+  }
+
+  /**
+   * Deletes elements starting from an index.
+   *
+   * @param {number} index Index at which to start deleting elements
+   * @param {number} [length=1] The number of elements to remove. Defaults to 1.
+   */
+  delete (index, length = 1) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListDelete(transaction, this, index, length)
+      })
+    } else {
+      // @ts-ignore _prelimContent is defined because this is not yet integrated
+      this._prelimContent.splice(index, length)
+    }
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @return {Array<YXmlElement|YXmlText|YXmlHook>}
+   */
+  toArray () {
+    return typeListToArray(this)
+  }
+
+  /**
+   * Appends content to this YArray.
+   *
+   * @param {Array<YXmlElement|YXmlText>} content Array of content to append.
+   */
+  push (content) {
+    this.insert(this.length, content)
+  }
+
+  /**
+   * Preppends content to this YArray.
+   *
+   * @param {Array<YXmlElement|YXmlText>} content Array of content to preppend.
+   */
+  unshift (content) {
+    this.insert(0, content)
+  }
+
+  /**
+   * Returns the i-th element from a YArray.
+   *
+   * @param {number} index The index of the element to return from the YArray
+   * @return {YXmlElement|YXmlText}
+   */
+  get (index) {
+    return typeListGet(this, index)
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @param {number} [start]
+   * @param {number} [end]
+   * @return {Array<YXmlElement|YXmlText>}
+   */
+  slice (start = 0, end = this.length) {
+    return typeListSlice(this, start, end)
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlFragmentRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlFragment}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlFragment = decoder => new YXmlFragment()
--- a/src/types/YXmlHook.js
+++ b/src/types/YXmlHook.js
@@ -0,0 +1,95 @@
+
+import {
+  YMap,
+  YXmlHookRefID,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2 // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * You can manage binding to a custom type with YXmlHook.
+ *
+ * @extends {YMap<any>}
+ */
+export class YXmlHook extends YMap {
+  /**
+   * @param {string} hookName nodeName of the Dom Node.
+   */
+  constructor (hookName) {
+    super()
+    /**
+     * @type {string}
+     */
+    this.hookName = hookName
+  }
+
+  /**
+   * Creates an Item with the same effect as this Item (without position effect)
+   */
+  _copy () {
+    return new YXmlHook(this.hookName)
+  }
+
+  /**
+   * @return {YXmlHook}
+   */
+  clone () {
+    const el = new YXmlHook(this.hookName)
+    this.forEach((value, key) => {
+      el.set(key, value)
+    })
+    return el
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlElement.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object.<string, any>} [hooks] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type
+   * @return {Element} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks = {}, binding) {
+    const hook = hooks[this.hookName]
+    let dom
+    if (hook !== undefined) {
+      dom = hook.createDom(this)
+    } else {
+      dom = document.createElement(this.hookName)
+    }
+    dom.setAttribute('data-yjs-hook', this.hookName)
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlHookRefID)
+    encoder.writeKey(this.hookName)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlHook}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlHook = decoder =>
+  new YXmlHook(decoder.readKey())
--- a/src/types/YXmlText.js
+++ b/src/types/YXmlText.js
@@ -0,0 +1,121 @@
+
+import {
+  YText,
+  YXmlTextRefID,
+  ContentType, YXmlElement, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * Represents text in a Dom Element. In the future this type will also handle
+ * simple formatting information like bold and italic.
+ */
+export class YXmlText extends YText {
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get nextSibling () {
+    const n = this._item ? this._item.next : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get prevSibling () {
+    const n = this._item ? this._item.prev : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  _copy () {
+    return new YXmlText()
+  }
+
+  /**
+   * @return {YXmlText}
+   */
+  clone () {
+    const text = new YXmlText()
+    text.applyDelta(this.toDelta())
+    return text
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlText.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object<string, any>} [hooks] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type.
+   * @return {Text} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks, binding) {
+    const dom = _document.createTextNode(this.toString())
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  toString () {
+    // @ts-ignore
+    return this.toDelta().map(delta => {
+      const nestedNodes = []
+      for (const nodeName in delta.attributes) {
+        const attrs = []
+        for (const key in delta.attributes[nodeName]) {
+          attrs.push({ key, value: delta.attributes[nodeName][key] })
+        }
+        // sort attributes to get a unique order
+        attrs.sort((a, b) => a.key < b.key ? -1 : 1)
+        nestedNodes.push({ nodeName, attrs })
+      }
+      // sort node order to get a unique order
+      nestedNodes.sort((a, b) => a.nodeName < b.nodeName ? -1 : 1)
+      // now convert to dom string
+      let str = ''
+      for (let i = 0; i < nestedNodes.length; i++) {
+        const node = nestedNodes[i]
+        str += `<${node.nodeName}`
+        for (let j = 0; j < node.attrs.length; j++) {
+          const attr = node.attrs[j]
+          str += ` ${attr.key}="${attr.value}"`
+        }
+        str += '>'
+      }
+      str += delta.insert
+      for (let i = nestedNodes.length - 1; i >= 0; i--) {
+        str += `</${nestedNodes[i].nodeName}>`
+      }
+      return str
+    }).join('')
+  }
+
+  /**
+   * @return {string}
+   */
+  toJSON () {
+    return this.toString()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlTextRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlText}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlText = decoder => new YXmlText()
--- a/src/utils/AbstractConnector.js
+++ b/src/utils/AbstractConnector.js
@@ -0,0 +1,26 @@
+
+import { Observable } from 'lib0/observable'
+
+import {
+  Doc // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * This is an abstract interface that all Connectors should implement to keep them interchangeable.
+ *
+ * @note This interface is experimental and it is not advised to actually inherit this class.
+ *       It just serves as typing information.
+ *
+ * @extends {Observable<any>}
+ */
+export class AbstractConnector extends Observable {
+  /**
+   * @param {Doc} ydoc
+   * @param {any} awareness
+   */
+  constructor (ydoc, awareness) {
+    super()
+    this.doc = ydoc
+    this.awareness = awareness
+  }
+}
--- a/src/utils/DeleteSet.js
+++ b/src/utils/DeleteSet.js
@@ -0,0 +1,326 @@
+
+import {
+  findIndexSS,
+  getState,
+  splitItem,
+  iterateStructs,
+  UpdateEncoderV2,
+  DSDecoderV1, DSEncoderV1, DSDecoderV2, DSEncoderV2, Item, GC, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+import * as array from 'lib0/array'
+import * as math from 'lib0/math'
+import * as map from 'lib0/map'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+
+export class DeleteItem {
+  /**
+   * @param {number} clock
+   * @param {number} len
+   */
+  constructor (clock, len) {
+    /**
+     * @type {number}
+     */
+    this.clock = clock
+    /**
+     * @type {number}
+     */
+    this.len = len
+  }
+}
+
+/**
+ * We no longer maintain a DeleteStore. DeleteSet is a temporary object that is created when needed.
+ * - When created in a transaction, it must only be accessed after sorting, and merging
+ *   - This DeleteSet is send to other clients
+ * - We do not create a DeleteSet when we send a sync message. The DeleteSet message is created directly from StructStore
+ * - We read a DeleteSet as part of a sync/update message. In this case the DeleteSet is already sorted and merged.
+ */
+export class DeleteSet {
+  constructor () {
+    /**
+     * @type {Map<number,Array<DeleteItem>>}
+     */
+    this.clients = new Map()
+  }
+}
+
+/**
+ * Iterate over all structs that the DeleteSet gc's.
+ *
+ * @param {Transaction} transaction
+ * @param {DeleteSet} ds
+ * @param {function(GC|Item):void} f
+ *
+ * @function
+ */
+export const iterateDeletedStructs = (transaction, ds, f) =>
+  ds.clients.forEach((deletes, clientid) => {
+    const structs = /** @type {Array<GC|Item>} */ (transaction.doc.store.clients.get(clientid))
+    for (let i = 0; i < deletes.length; i++) {
+      const del = deletes[i]
+      iterateStructs(transaction, structs, del.clock, del.len, f)
+    }
+  })
+
+/**
+ * @param {Array<DeleteItem>} dis
+ * @param {number} clock
+ * @return {number|null}
+ *
+ * @private
+ * @function
+ */
+export const findIndexDS = (dis, clock) => {
+  let left = 0
+  let right = dis.length - 1
+  while (left <= right) {
+    const midindex = math.floor((left + right) / 2)
+    const mid = dis[midindex]
+    const midclock = mid.clock
+    if (midclock <= clock) {
+      if (clock < midclock + mid.len) {
+        return midindex
+      }
+      left = midindex + 1
+    } else {
+      right = midindex - 1
+    }
+  }
+  return null
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {ID} id
+ * @return {boolean}
+ *
+ * @private
+ * @function
+ */
+export const isDeleted = (ds, id) => {
+  const dis = ds.clients.get(id.client)
+  return dis !== undefined && findIndexDS(dis, id.clock) !== null
+}
+
+/**
+ * @param {DeleteSet} ds
+ *
+ * @private
+ * @function
+ */
+export const sortAndMergeDeleteSet = ds => {
+  ds.clients.forEach(dels => {
+    dels.sort((a, b) => a.clock - b.clock)
+    // merge items without filtering or splicing the array
+    // i is the current pointer
+    // j refers to the current insert position for the pointed item
+    // try to merge dels[i] into dels[j-1] or set dels[j]=dels[i]
+    let i, j
+    for (i = 1, j = 1; i < dels.length; i++) {
+      const left = dels[j - 1]
+      const right = dels[i]
+      if (left.clock + left.len >= right.clock) {
+        left.len = math.max(left.len, right.clock + right.len - left.clock)
+      } else {
+        if (j < i) {
+          dels[j] = right
+        }
+        j++
+      }
+    }
+    dels.length = j
+  })
+}
+
+/**
+ * @param {Array<DeleteSet>} dss
+ * @return {DeleteSet} A fresh DeleteSet
+ */
+export const mergeDeleteSets = dss => {
+  const merged = new DeleteSet()
+  for (let dssI = 0; dssI < dss.length; dssI++) {
+    dss[dssI].clients.forEach((delsLeft, client) => {
+      if (!merged.clients.has(client)) {
+        // Write all missing keys from current ds and all following.
+        // If merged already contains `client` current ds has already been added.
+        /**
+         * @type {Array<DeleteItem>}
+         */
+        const dels = delsLeft.slice()
+        for (let i = dssI + 1; i < dss.length; i++) {
+          array.appendTo(dels, dss[i].clients.get(client) || [])
+        }
+        merged.clients.set(client, dels)
+      }
+    })
+  }
+  sortAndMergeDeleteSet(merged)
+  return merged
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {number} client
+ * @param {number} clock
+ * @param {number} length
+ *
+ * @private
+ * @function
+ */
+export const addToDeleteSet = (ds, client, clock, length) => {
+  map.setIfUndefined(ds.clients, client, () => []).push(new DeleteItem(clock, length))
+}
+
+export const createDeleteSet = () => new DeleteSet()
+
+/**
+ * @param {StructStore} ss
+ * @return {DeleteSet} Merged and sorted DeleteSet
+ *
+ * @private
+ * @function
+ */
+export const createDeleteSetFromStructStore = ss => {
+  const ds = createDeleteSet()
+  ss.clients.forEach((structs, client) => {
+    /**
+     * @type {Array<DeleteItem>}
+     */
+    const dsitems = []
+    for (let i = 0; i < structs.length; i++) {
+      const struct = structs[i]
+      if (struct.deleted) {
+        const clock = struct.id.clock
+        let len = struct.length
+        if (i + 1 < structs.length) {
+          for (let next = structs[i + 1]; i + 1 < structs.length && next.deleted; next = structs[++i + 1]) {
+            len += next.length
+          }
+        }
+        dsitems.push(new DeleteItem(clock, len))
+      }
+    }
+    if (dsitems.length > 0) {
+      ds.clients.set(client, dsitems)
+    }
+  })
+  return ds
+}
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {DeleteSet} ds
+ *
+ * @private
+ * @function
+ */
+export const writeDeleteSet = (encoder, ds) => {
+  encoding.writeVarUint(encoder.restEncoder, ds.clients.size)
+  ds.clients.forEach((dsitems, client) => {
+    encoder.resetDsCurVal()
+    encoding.writeVarUint(encoder.restEncoder, client)
+    const len = dsitems.length
+    encoding.writeVarUint(encoder.restEncoder, len)
+    for (let i = 0; i < len; i++) {
+      const item = dsitems[i]
+      encoder.writeDsClock(item.clock)
+      encoder.writeDsLen(item.len)
+    }
+  })
+}
+
+/**
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @return {DeleteSet}
+ *
+ * @private
+ * @function
+ */
+export const readDeleteSet = decoder => {
+  const ds = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numClients; i++) {
+    decoder.resetDsCurVal()
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const numberOfDeletes = decoding.readVarUint(decoder.restDecoder)
+    if (numberOfDeletes > 0) {
+      const dsField = map.setIfUndefined(ds.clients, client, () => [])
+      for (let i = 0; i < numberOfDeletes; i++) {
+        dsField.push(new DeleteItem(decoder.readDsClock(), decoder.readDsLen()))
+      }
+    }
+  }
+  return ds
+}
+
+/**
+ * @todo YDecoder also contains references to String and other Decoders. Would make sense to exchange YDecoder.toUint8Array for YDecoder.DsToUint8Array()..
+ */
+
+/**
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @return {Uint8Array|null} Returns a v2 update containing all deletes that couldn't be applied yet; or null if all deletes were applied successfully.
+ *
+ * @private
+ * @function
+ */
+export const readAndApplyDeleteSet = (decoder, transaction, store) => {
+  const unappliedDS = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numClients; i++) {
+    decoder.resetDsCurVal()
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const numberOfDeletes = decoding.readVarUint(decoder.restDecoder)
+    const structs = store.clients.get(client) || []
+    const state = getState(store, client)
+    for (let i = 0; i < numberOfDeletes; i++) {
+      const clock = decoder.readDsClock()
+      const clockEnd = clock + decoder.readDsLen()
+      if (clock < state) {
+        if (state < clockEnd) {
+          addToDeleteSet(unappliedDS, client, state, clockEnd - state)
+        }
+        let index = findIndexSS(structs, clock)
+        /**
+         * We can ignore the case of GC and Delete structs, because we are going to skip them
+         * @type {Item}
+         */
+        // @ts-ignore
+        let struct = structs[index]
+        // split the first item if necessary
+        if (!struct.deleted && struct.id.clock < clock) {
+          structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock))
+          index++ // increase we now want to use the next struct
+        }
+        while (index < structs.length) {
+          // @ts-ignore
+          struct = structs[index++]
+          if (struct.id.clock < clockEnd) {
+            if (!struct.deleted) {
+              if (clockEnd < struct.id.clock + struct.length) {
+                structs.splice(index, 0, splitItem(transaction, struct, clockEnd - struct.id.clock))
+              }
+              struct.delete(transaction)
+            }
+          } else {
+            break
+          }
+        }
+      } else {
+        addToDeleteSet(unappliedDS, client, clock, clockEnd - clock)
+      }
+    }
+  }
+  if (unappliedDS.clients.size > 0) {
+    const ds = new UpdateEncoderV2()
+    encoding.writeVarUint(ds.restEncoder, 0) // encode 0 structs
+    writeDeleteSet(ds, unappliedDS)
+    return ds.toUint8Array()
+  }
+  return null
+}
--- a/src/utils/Doc.js
+++ b/src/utils/Doc.js
@@ -0,0 +1,285 @@
+/**
+ * @module Y
+ */
+
+import {
+  StructStore,
+  AbstractType,
+  YArray,
+  YText,
+  YMap,
+  YXmlFragment,
+  transact,
+  ContentDoc, Item, Transaction, YEvent // eslint-disable-line
+} from '../internals.js'
+
+import { Observable } from 'lib0/observable'
+import * as random from 'lib0/random'
+import * as map from 'lib0/map'
+import * as array from 'lib0/array'
+
+export const generateNewClientId = random.uint32
+
+/**
+ * @typedef {Object} DocOpts
+ * @property {boolean} [DocOpts.gc=true] Disable garbage collection (default: gc=true)
+ * @property {function(Item):boolean} [DocOpts.gcFilter] Will be called before an Item is garbage collected. Return false to keep the Item.
+ * @property {string} [DocOpts.guid] Define a globally unique identifier for this document
+ * @property {string | null} [DocOpts.collectionid] Associate this document with a collection. This only plays a role if your provider has a concept of collection.
+ * @property {any} [DocOpts.meta] Any kind of meta information you want to associate with this document. If this is a subdocument, remote peers will store the meta information as well.
+ * @property {boolean} [DocOpts.autoLoad] If a subdocument, automatically load document. If this is a subdocument, remote peers will load the document as well automatically.
+ */
+
+/**
+ * A Yjs instance handles the state of shared data.
+ * @extends Observable<string>
+ */
+export class Doc extends Observable {
+  /**
+   * @param {DocOpts} [opts] configuration
+   */
+  constructor ({ guid = random.uuidv4(), collectionid = null, gc = true, gcFilter = () => true, meta = null, autoLoad = false } = {}) {
+    super()
+    this.gc = gc
+    this.gcFilter = gcFilter
+    this.clientID = generateNewClientId()
+    this.guid = guid
+    this.collectionid = collectionid
+    /**
+     * @type {Map<string, AbstractType<YEvent>>}
+     */
+    this.share = new Map()
+    this.store = new StructStore()
+    /**
+     * @type {Transaction | null}
+     */
+    this._transaction = null
+    /**
+     * @type {Array<Transaction>}
+     */
+    this._transactionCleanups = []
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocs = new Set()
+    /**
+     * If this document is a subdocument - a document integrated into another document - then _item is defined.
+     * @type {Item?}
+     */
+    this._item = null
+    this.shouldLoad = autoLoad
+    this.autoLoad = autoLoad
+    this.meta = meta
+  }
+
+  /**
+   * Notify the parent document that you request to load data into this subdocument (if it is a subdocument).
+   *
+   * `load()` might be used in the future to request any provider to load the most current data.
+   *
+   * It is safe to call `load()` multiple times.
+   */
+  load () {
+    const item = this._item
+    if (item !== null && !this.shouldLoad) {
+      transact(/** @type {any} */ (item.parent).doc, transaction => {
+        transaction.subdocsLoaded.add(this)
+      }, null, true)
+    }
+    this.shouldLoad = true
+  }
+
+  getSubdocs () {
+    return this.subdocs
+  }
+
+  getSubdocGuids () {
+    return new Set(Array.from(this.subdocs).map(doc => doc.guid))
+  }
+
+  /**
+   * Changes that happen inside of a transaction are bundled. This means that
+   * the observer fires _after_ the transaction is finished and that all changes
+   * that happened inside of the transaction are sent as one message to the
+   * other peers.
+   *
+   * @param {function(Transaction):void} f The function that should be executed as a transaction
+   * @param {any} [origin] Origin of who started the transaction. Will be stored on transaction.origin
+   *
+   * @public
+   */
+  transact (f, origin = null) {
+    transact(this, f, origin)
+  }
+
+  /**
+   * Define a shared data type.
+   *
+   * Multiple calls of `y.get(name, TypeConstructor)` yield the same result
+   * and do not overwrite each other. I.e.
+   * `y.define(name, Y.Array) === y.define(name, Y.Array)`
+   *
+   * After this method is called, the type is also available on `y.share.get(name)`.
+   *
+   * *Best Practices:*
+   * Define all types right after the Yjs instance is created and store them in a separate object.
+   * Also use the typed methods `getText(name)`, `getArray(name)`, ..
+   *
+   * @example
+   *   const y = new Y(..)
+   *   const appState = {
+   *     document: y.getText('document')
+   *     comments: y.getArray('comments')
+   *   }
+   *
+   * @param {string} name
+   * @param {Function} TypeConstructor The constructor of the type definition. E.g. Y.Text, Y.Array, Y.Map, ...
+   * @return {AbstractType<any>} The created type. Constructed with TypeConstructor
+   *
+   * @public
+   */
+  get (name, TypeConstructor = AbstractType) {
+    const type = map.setIfUndefined(this.share, name, () => {
+      // @ts-ignore
+      const t = new TypeConstructor()
+      t._integrate(this, null)
+      return t
+    })
+    const Constr = type.constructor
+    if (TypeConstructor !== AbstractType && Constr !== TypeConstructor) {
+      if (Constr === AbstractType) {
+        // @ts-ignore
+        const t = new TypeConstructor()
+        t._map = type._map
+        type._map.forEach(/** @param {Item?} n */ n => {
+          for (; n !== null; n = n.left) {
+            // @ts-ignore
+            n.parent = t
+          }
+        })
+        t._start = type._start
+        for (let n = t._start; n !== null; n = n.right) {
+          n.parent = t
+        }
+        t._length = type._length
+        this.share.set(name, t)
+        t._integrate(this, null)
+        return t
+      } else {
+        throw new Error(`Type with the name ${name} has already been defined with a different constructor`)
+      }
+    }
+    return type
+  }
+
+  /**
+   * @template T
+   * @param {string} [name]
+   * @return {YArray<T>}
+   *
+   * @public
+   */
+  getArray (name = '') {
+    // @ts-ignore
+    return this.get(name, YArray)
+  }
+
+  /**
+   * @param {string} [name]
+   * @return {YText}
+   *
+   * @public
+   */
+  getText (name = '') {
+    // @ts-ignore
+    return this.get(name, YText)
+  }
+
+  /**
+   * @template T
+   * @param {string} [name]
+   * @return {YMap<T>}
+   *
+   * @public
+   */
+  getMap (name = '') {
+    // @ts-ignore
+    return this.get(name, YMap)
+  }
+
+  /**
+   * @param {string} [name]
+   * @return {YXmlFragment}
+   *
+   * @public
+   */
+  getXmlFragment (name = '') {
+    // @ts-ignore
+    return this.get(name, YXmlFragment)
+  }
+
+  /**
+   * Converts the entire document into a js object, recursively traversing each yjs type
+   * Doesn't log types that have not been defined (using ydoc.getType(..)).
+   *
+   * @deprecated Do not use this method and rather call toJSON directly on the shared types.
+   *
+   * @return {Object<string, any>}
+   */
+  toJSON () {
+    /**
+     * @type {Object<string, any>}
+     */
+    const doc = {}
+
+    this.share.forEach((value, key) => {
+      doc[key] = value.toJSON()
+    })
+
+    return doc
+  }
+
+  /**
+   * Emit `destroy` event and unregister all event handlers.
+   */
+  destroy () {
+    array.from(this.subdocs).forEach(subdoc => subdoc.destroy())
+    const item = this._item
+    if (item !== null) {
+      this._item = null
+      const content = /** @type {ContentDoc} */ (item.content)
+      if (item.deleted) {
+        // @ts-ignore
+        content.doc = null
+      } else {
+        content.doc = new Doc({ guid: this.guid, ...content.opts })
+        content.doc._item = item
+      }
+      transact(/** @type {any} */ (item).parent.doc, transaction => {
+        if (!item.deleted) {
+          transaction.subdocsAdded.add(content.doc)
+        }
+        transaction.subdocsRemoved.add(this)
+      }, null, true)
+    }
+    this.emit('destroyed', [true])
+    this.emit('destroy', [this])
+    super.destroy()
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {function(...any):any} f
+   */
+  on (eventName, f) {
+    super.on(eventName, f)
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {function} f
+   */
+  off (eventName, f) {
+    super.off(eventName, f)
+  }
+}
--- a/src/utils/EventHandler.js
+++ b/src/utils/EventHandler.js
@@ -0,0 +1,87 @@
+import * as f from 'lib0/function'
+
+/**
+ * General event handler implementation.
+ *
+ * @template ARG0, ARG1
+ *
+ * @private
+ */
+export class EventHandler {
+  constructor () {
+    /**
+     * @type {Array<function(ARG0, ARG1):void>}
+     */
+    this.l = []
+  }
+}
+
+/**
+ * @template ARG0,ARG1
+ * @returns {EventHandler<ARG0,ARG1>}
+ *
+ * @private
+ * @function
+ */
+export const createEventHandler = () => new EventHandler()
+
+/**
+ * Adds an event listener that is called when
+ * {@link EventHandler#callEventListeners} is called.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {function(ARG0,ARG1):void} f The event handler.
+ *
+ * @private
+ * @function
+ */
+export const addEventHandlerListener = (eventHandler, f) =>
+  eventHandler.l.push(f)
+
+/**
+ * Removes an event listener.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {function(ARG0,ARG1):void} f The event handler that was added with
+ *                     {@link EventHandler#addEventListener}
+ *
+ * @private
+ * @function
+ */
+export const removeEventHandlerListener = (eventHandler, f) => {
+  const l = eventHandler.l
+  const len = l.length
+  eventHandler.l = l.filter(g => f !== g)
+  if (len === eventHandler.l.length) {
+    console.error('[yjs] Tried to remove event handler that doesn\'t exist.')
+  }
+}
+
+/**
+ * Removes all event listeners.
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ *
+ * @private
+ * @function
+ */
+export const removeAllEventHandlerListeners = eventHandler => {
+  eventHandler.l.length = 0
+}
+
+/**
+ * Call all event listeners that were added via
+ * {@link EventHandler#addEventListener}.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {ARG0} arg0
+ * @param {ARG1} arg1
+ *
+ * @private
+ * @function
+ */
+export const callEventHandlerListeners = (eventHandler, arg0, arg1) =>
+  f.callAll(eventHandler.l, [arg0, arg1])
--- a/src/utils/ID.js
+++ b/src/utils/ID.js
@@ -0,0 +1,90 @@
+
+import { AbstractType } from '../internals.js' // eslint-disable-line
+
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+import * as error from 'lib0/error'
+
+export class ID {
+  /**
+   * @param {number} client client id
+   * @param {number} clock unique per client id, continuous number
+   */
+  constructor (client, clock) {
+    /**
+     * Client id
+     * @type {number}
+     */
+    this.client = client
+    /**
+     * unique per client id, continuous number
+     * @type {number}
+     */
+    this.clock = clock
+  }
+}
+
+/**
+ * @param {ID | null} a
+ * @param {ID | null} b
+ * @return {boolean}
+ *
+ * @function
+ */
+export const compareIDs = (a, b) => a === b || (a !== null && b !== null && a.client === b.client && a.clock === b.clock)
+
+/**
+ * @param {number} client
+ * @param {number} clock
+ *
+ * @private
+ * @function
+ */
+export const createID = (client, clock) => new ID(client, clock)
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {ID} id
+ *
+ * @private
+ * @function
+ */
+export const writeID = (encoder, id) => {
+  encoding.writeVarUint(encoder, id.client)
+  encoding.writeVarUint(encoder, id.clock)
+}
+
+/**
+ * Read ID.
+ * * If first varUint read is 0xFFFFFF a RootID is returned.
+ * * Otherwise an ID is returned
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ID}
+ *
+ * @private
+ * @function
+ */
+export const readID = decoder =>
+  createID(decoding.readVarUint(decoder), decoding.readVarUint(decoder))
+
+/**
+ * The top types are mapped from y.share.get(keyname) => type.
+ * `type` does not store any information about the `keyname`.
+ * This function finds the correct `keyname` for `type` and throws otherwise.
+ *
+ * @param {AbstractType<any>} type
+ * @return {string}
+ *
+ * @private
+ * @function
+ */
+export const findRootTypeKey = type => {
+  // @ts-ignore _y must be defined, otherwise unexpected case
+  for (const [key, value] of type.doc.share.entries()) {
+    if (value === type) {
+      return key
+    }
+  }
+  throw error.unexpectedCase()
+}
--- a/src/utils/PermanentUserData.js
+++ b/src/utils/PermanentUserData.js
@@ -0,0 +1,142 @@
+
+import {
+  YArray,
+  YMap,
+  readDeleteSet,
+  writeDeleteSet,
+  createDeleteSet,
+  DSEncoderV1, DSDecoderV1, ID, DeleteSet, YArrayEvent, Transaction, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding'
+
+import { mergeDeleteSets, isDeleted } from './DeleteSet.js'
+
+export class PermanentUserData {
+  /**
+   * @param {Doc} doc
+   * @param {YMap<any>} [storeType]
+   */
+  constructor (doc, storeType = doc.getMap('users')) {
+    /**
+     * @type {Map<string,DeleteSet>}
+     */
+    const dss = new Map()
+    this.yusers = storeType
+    this.doc = doc
+    /**
+     * Maps from clientid to userDescription
+     *
+     * @type {Map<number,string>}
+     */
+    this.clients = new Map()
+    this.dss = dss
+    /**
+     * @param {YMap<any>} user
+     * @param {string} userDescription
+     */
+    const initUser = (user, userDescription) => {
+      /**
+       * @type {YArray<Uint8Array>}
+       */
+      const ds = user.get('ds')
+      const ids = user.get('ids')
+      const addClientId = /** @param {number} clientid */ clientid => this.clients.set(clientid, userDescription)
+      ds.observe(/** @param {YArrayEvent<any>} event */ event => {
+        event.changes.added.forEach(item => {
+          item.content.getContent().forEach(encodedDs => {
+            if (encodedDs instanceof Uint8Array) {
+              this.dss.set(userDescription, mergeDeleteSets([this.dss.get(userDescription) || createDeleteSet(), readDeleteSet(new DSDecoderV1(decoding.createDecoder(encodedDs)))]))
+            }
+          })
+        })
+      })
+      this.dss.set(userDescription, mergeDeleteSets(ds.map(encodedDs => readDeleteSet(new DSDecoderV1(decoding.createDecoder(encodedDs))))))
+      ids.observe(/** @param {YArrayEvent<any>} event */ event =>
+        event.changes.added.forEach(item => item.content.getContent().forEach(addClientId))
+      )
+      ids.forEach(addClientId)
+    }
+    // observe users
+    storeType.observe(event => {
+      event.keysChanged.forEach(userDescription =>
+        initUser(storeType.get(userDescription), userDescription)
+      )
+    })
+    // add intial data
+    storeType.forEach(initUser)
+  }
+
+  /**
+   * @param {Doc} doc
+   * @param {number} clientid
+   * @param {string} userDescription
+   * @param {Object} [conf]
+   * @param {function(Transaction, DeleteSet):boolean} [conf.filter]
+   */
+  setUserMapping (doc, clientid, userDescription, { filter = () => true } = {}) {
+    const users = this.yusers
+    let user = users.get(userDescription)
+    if (!user) {
+      user = new YMap()
+      user.set('ids', new YArray())
+      user.set('ds', new YArray())
+      users.set(userDescription, user)
+    }
+    user.get('ids').push([clientid])
+    users.observe(event => {
+      setTimeout(() => {
+        const userOverwrite = users.get(userDescription)
+        if (userOverwrite !== user) {
+          // user was overwritten, port all data over to the next user object
+          // @todo Experiment with Y.Sets here
+          user = userOverwrite
+          // @todo iterate over old type
+          this.clients.forEach((_userDescription, clientid) => {
+            if (userDescription === _userDescription) {
+              user.get('ids').push([clientid])
+            }
+          })
+          const encoder = new DSEncoderV1()
+          const ds = this.dss.get(userDescription)
+          if (ds) {
+            writeDeleteSet(encoder, ds)
+            user.get('ds').push([encoder.toUint8Array()])
+          }
+        }
+      }, 0)
+    })
+    doc.on('afterTransaction', /** @param {Transaction} transaction */ transaction => {
+      setTimeout(() => {
+        const yds = user.get('ds')
+        const ds = transaction.deleteSet
+        if (transaction.local && ds.clients.size > 0 && filter(transaction, ds)) {
+          const encoder = new DSEncoderV1()
+          writeDeleteSet(encoder, ds)
+          yds.push([encoder.toUint8Array()])
+        }
+      })
+    })
+  }
+
+  /**
+   * @param {number} clientid
+   * @return {any}
+   */
+  getUserByClientId (clientid) {
+    return this.clients.get(clientid) || null
+  }
+
+  /**
+   * @param {ID} id
+   * @return {string | null}
+   */
+  getUserByDeletedId (id) {
+    for (const [userDescription, ds] of this.dss.entries()) {
+      if (isDeleted(ds, id)) {
+        return userDescription
+      }
+    }
+    return null
+  }
+}
--- a/src/utils/RelativePosition.js
+++ b/src/utils/RelativePosition.js
@@ -0,0 +1,330 @@
+
+import {
+  writeID,
+  readID,
+  compareIDs,
+  getState,
+  findRootTypeKey,
+  Item,
+  createID,
+  ContentType,
+  followRedone,
+  ID, Doc, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as error from 'lib0/error'
+
+/**
+ * A relative position is based on the Yjs model and is not affected by document changes.
+ * E.g. If you place a relative position before a certain character, it will always point to this character.
+ * If you place a relative position at the end of a type, it will always point to the end of the type.
+ *
+ * A numeric position is often unsuited for user selections, because it does not change when content is inserted
+ * before or after.
+ *
+ * ```Insert(0, 'x')('a|bc') = 'xa|bc'``` Where | is the relative position.
+ *
+ * One of the properties must be defined.
+ *
+ * @example
+ *   // Current cursor position is at position 10
+ *   const relativePosition = createRelativePositionFromIndex(yText, 10)
+ *   // modify yText
+ *   yText.insert(0, 'abc')
+ *   yText.delete(3, 10)
+ *   // Compute the cursor position
+ *   const absolutePosition = createAbsolutePositionFromRelativePosition(y, relativePosition)
+ *   absolutePosition.type === yText // => true
+ *   console.log('cursor location is ' + absolutePosition.index) // => cursor location is 3
+ *
+ */
+export class RelativePosition {
+  /**
+   * @param {ID|null} type
+   * @param {string|null} tname
+   * @param {ID|null} item
+   * @param {number} assoc
+   */
+  constructor (type, tname, item, assoc = 0) {
+    /**
+     * @type {ID|null}
+     */
+    this.type = type
+    /**
+     * @type {string|null}
+     */
+    this.tname = tname
+    /**
+     * @type {ID | null}
+     */
+    this.item = item
+    /**
+     * A relative position is associated to a specific character. By default
+     * assoc >= 0, the relative position is associated to the character
+     * after the meant position.
+     * I.e. position 1 in 'ab' is associated to character 'b'.
+     *
+     * If assoc < 0, then the relative position is associated to the caharacter
+     * before the meant position.
+     *
+     * @type {number}
+     */
+    this.assoc = assoc
+  }
+}
+
+/**
+ * @param {RelativePosition} rpos
+ * @return {any}
+ */
+export const relativePositionToJSON = rpos => {
+  const json = {}
+  if (rpos.type) {
+    json.type = rpos.type
+  }
+  if (rpos.tname) {
+    json.tname = rpos.tname
+  }
+  if (rpos.item) {
+    json.item = rpos.item
+  }
+  if (rpos.assoc != null) {
+    json.assoc = rpos.assoc
+  }
+  return json
+}
+
+/**
+ * @param {any} json
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const createRelativePositionFromJSON = json => new RelativePosition(json.type == null ? null : createID(json.type.client, json.type.clock), json.tname || null, json.item == null ? null : createID(json.item.client, json.item.clock), json.assoc == null ? 0 : json.assoc)
+
+export class AbsolutePosition {
+  /**
+   * @param {AbstractType<any>} type
+   * @param {number} index
+   * @param {number} [assoc]
+   */
+  constructor (type, index, assoc = 0) {
+    /**
+     * @type {AbstractType<any>}
+     */
+    this.type = type
+    /**
+     * @type {number}
+     */
+    this.index = index
+    this.assoc = assoc
+  }
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} index
+ * @param {number} [assoc]
+ *
+ * @function
+ */
+export const createAbsolutePosition = (type, index, assoc = 0) => new AbsolutePosition(type, index, assoc)
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {ID|null} item
+ * @param {number} [assoc]
+ *
+ * @function
+ */
+export const createRelativePosition = (type, item, assoc) => {
+  let typeid = null
+  let tname = null
+  if (type._item === null) {
+    tname = findRootTypeKey(type)
+  } else {
+    typeid = createID(type._item.id.client, type._item.id.clock)
+  }
+  return new RelativePosition(typeid, tname, item, assoc)
+}
+
+/**
+ * Create a relativePosition based on a absolute position.
+ *
+ * @param {AbstractType<any>} type The base type (e.g. YText or YArray).
+ * @param {number} index The absolute position.
+ * @param {number} [assoc]
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const createRelativePositionFromTypeIndex = (type, index, assoc = 0) => {
+  let t = type._start
+  if (assoc < 0) {
+    // associated to the left character or the beginning of a type, increment index if possible.
+    if (index === 0) {
+      return createRelativePosition(type, null, assoc)
+    }
+    index--
+  }
+  while (t !== null) {
+    if (!t.deleted && t.countable) {
+      if (t.length > index) {
+        // case 1: found position somewhere in the linked list
+        return createRelativePosition(type, createID(t.id.client, t.id.clock + index), assoc)
+      }
+      index -= t.length
+    }
+    if (t.right === null && assoc < 0) {
+      // left-associated position, return last available id
+      return createRelativePosition(type, t.lastId, assoc)
+    }
+    t = t.right
+  }
+  return createRelativePosition(type, null, assoc)
+}
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {RelativePosition} rpos
+ *
+ * @function
+ */
+export const writeRelativePosition = (encoder, rpos) => {
+  const { type, tname, item, assoc } = rpos
+  if (item !== null) {
+    encoding.writeVarUint(encoder, 0)
+    writeID(encoder, item)
+  } else if (tname !== null) {
+    // case 2: found position at the end of the list and type is stored in y.share
+    encoding.writeUint8(encoder, 1)
+    encoding.writeVarString(encoder, tname)
+  } else if (type !== null) {
+    // case 3: found position at the end of the list and type is attached to an item
+    encoding.writeUint8(encoder, 2)
+    writeID(encoder, type)
+  } else {
+    throw error.unexpectedCase()
+  }
+  encoding.writeVarInt(encoder, assoc)
+  return encoder
+}
+
+/**
+ * @param {RelativePosition} rpos
+ * @return {Uint8Array}
+ */
+export const encodeRelativePosition = rpos => {
+  const encoder = encoding.createEncoder()
+  writeRelativePosition(encoder, rpos)
+  return encoding.toUint8Array(encoder)
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const readRelativePosition = decoder => {
+  let type = null
+  let tname = null
+  let itemID = null
+  switch (decoding.readVarUint(decoder)) {
+    case 0:
+      // case 1: found position somewhere in the linked list
+      itemID = readID(decoder)
+      break
+    case 1:
+      // case 2: found position at the end of the list and type is stored in y.share
+      tname = decoding.readVarString(decoder)
+      break
+    case 2: {
+      // case 3: found position at the end of the list and type is attached to an item
+      type = readID(decoder)
+    }
+  }
+  const assoc = decoding.hasContent(decoder) ? decoding.readVarInt(decoder) : 0
+  return new RelativePosition(type, tname, itemID, assoc)
+}
+
+/**
+ * @param {Uint8Array} uint8Array
+ * @return {RelativePosition}
+ */
+export const decodeRelativePosition = uint8Array => readRelativePosition(decoding.createDecoder(uint8Array))
+
+/**
+ * @param {RelativePosition} rpos
+ * @param {Doc} doc
+ * @return {AbsolutePosition|null}
+ *
+ * @function
+ */
+export const createAbsolutePositionFromRelativePosition = (rpos, doc) => {
+  const store = doc.store
+  const rightID = rpos.item
+  const typeID = rpos.type
+  const tname = rpos.tname
+  const assoc = rpos.assoc
+  let type = null
+  let index = 0
+  if (rightID !== null) {
+    if (getState(store, rightID.client) <= rightID.clock) {
+      return null
+    }
+    const res = followRedone(store, rightID)
+    const right = res.item
+    if (!(right instanceof Item)) {
+      return null
+    }
+    type = /** @type {AbstractType<any>} */ (right.parent)
+    if (type._item === null || !type._item.deleted) {
+      index = (right.deleted || !right.countable) ? 0 : (res.diff + (assoc >= 0 ? 0 : 1)) // adjust position based on left association if necessary
+      let n = right.left
+      while (n !== null) {
+        if (!n.deleted && n.countable) {
+          index += n.length
+        }
+        n = n.left
+      }
+    }
+  } else {
+    if (tname !== null) {
+      type = doc.get(tname)
+    } else if (typeID !== null) {
+      if (getState(store, typeID.client) <= typeID.clock) {
+        // type does not exist yet
+        return null
+      }
+      const { item } = followRedone(store, typeID)
+      if (item instanceof Item && item.content instanceof ContentType) {
+        type = item.content.type
+      } else {
+        // struct is garbage collected
+        return null
+      }
+    } else {
+      throw error.unexpectedCase()
+    }
+    if (assoc >= 0) {
+      index = type._length
+    } else {
+      index = 0
+    }
+  }
+  return createAbsolutePosition(type, index, rpos.assoc)
+}
+
+/**
+ * @param {RelativePosition|null} a
+ * @param {RelativePosition|null} b
+ * @return {boolean}
+ *
+ * @function
+ */
+export const compareRelativePositions = (a, b) => a === b || (
+  a !== null && b !== null && a.tname === b.tname && compareIDs(a.item, b.item) && compareIDs(a.type, b.type) && a.assoc === b.assoc
+)
--- a/src/utils/Snapshot.js
+++ b/src/utils/Snapshot.js
@@ -0,0 +1,201 @@
+
+import {
+  isDeleted,
+  createDeleteSetFromStructStore,
+  getStateVector,
+  getItemCleanStart,
+  iterateDeletedStructs,
+  writeDeleteSet,
+  writeStateVector,
+  readDeleteSet,
+  readStateVector,
+  createDeleteSet,
+  createID,
+  getState,
+  findIndexSS,
+  UpdateEncoderV2,
+  applyUpdateV2,
+  DSEncoderV1, DSEncoderV2, DSDecoderV1, DSDecoderV2, Transaction, Doc, DeleteSet, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as set from 'lib0/set'
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+
+export class Snapshot {
+  /**
+   * @param {DeleteSet} ds
+   * @param {Map<number,number>} sv state map
+   */
+  constructor (ds, sv) {
+    /**
+     * @type {DeleteSet}
+     */
+    this.ds = ds
+    /**
+     * State Map
+     * @type {Map<number,number>}
+     */
+    this.sv = sv
+  }
+}
+
+/**
+ * @param {Snapshot} snap1
+ * @param {Snapshot} snap2
+ * @return {boolean}
+ */
+export const equalSnapshots = (snap1, snap2) => {
+  const ds1 = snap1.ds.clients
+  const ds2 = snap2.ds.clients
+  const sv1 = snap1.sv
+  const sv2 = snap2.sv
+  if (sv1.size !== sv2.size || ds1.size !== ds2.size) {
+    return false
+  }
+  for (const [key, value] of sv1.entries()) {
+    if (sv2.get(key) !== value) {
+      return false
+    }
+  }
+  for (const [client, dsitems1] of ds1.entries()) {
+    const dsitems2 = ds2.get(client) || []
+    if (dsitems1.length !== dsitems2.length) {
+      return false
+    }
+    for (let i = 0; i < dsitems1.length; i++) {
+      const dsitem1 = dsitems1[i]
+      const dsitem2 = dsitems2[i]
+      if (dsitem1.clock !== dsitem2.clock || dsitem1.len !== dsitem2.len) {
+        return false
+      }
+    }
+  }
+  return true
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {DSEncoderV1 | DSEncoderV2} [encoder]
+ * @return {Uint8Array}
+ */
+export const encodeSnapshotV2 = (snapshot, encoder = new DSEncoderV2()) => {
+  writeDeleteSet(encoder, snapshot.ds)
+  writeStateVector(encoder, snapshot.sv)
+  return encoder.toUint8Array()
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @return {Uint8Array}
+ */
+export const encodeSnapshot = snapshot => encodeSnapshotV2(snapshot, new DSEncoderV1())
+
+/**
+ * @param {Uint8Array} buf
+ * @param {DSDecoderV1 | DSDecoderV2} [decoder]
+ * @return {Snapshot}
+ */
+export const decodeSnapshotV2 = (buf, decoder = new DSDecoderV2(decoding.createDecoder(buf))) => {
+  return new Snapshot(readDeleteSet(decoder), readStateVector(decoder))
+}
+
+/**
+ * @param {Uint8Array} buf
+ * @return {Snapshot}
+ */
+export const decodeSnapshot = buf => decodeSnapshotV2(buf, new DSDecoderV1(decoding.createDecoder(buf)))
+
+/**
+ * @param {DeleteSet} ds
+ * @param {Map<number,number>} sm
+ * @return {Snapshot}
+ */
+export const createSnapshot = (ds, sm) => new Snapshot(ds, sm)
+
+export const emptySnapshot = createSnapshot(createDeleteSet(), new Map())
+
+/**
+ * @param {Doc} doc
+ * @return {Snapshot}
+ */
+export const snapshot = doc => createSnapshot(createDeleteSetFromStructStore(doc.store), getStateVector(doc.store))
+
+/**
+ * @param {Item} item
+ * @param {Snapshot|undefined} snapshot
+ *
+ * @protected
+ * @function
+ */
+export const isVisible = (item, snapshot) => snapshot === undefined
+  ? !item.deleted
+  : snapshot.sv.has(item.id.client) && (snapshot.sv.get(item.id.client) || 0) > item.id.clock && !isDeleted(snapshot.ds, item.id)
+
+/**
+ * @param {Transaction} transaction
+ * @param {Snapshot} snapshot
+ */
+export const splitSnapshotAffectedStructs = (transaction, snapshot) => {
+  const meta = map.setIfUndefined(transaction.meta, splitSnapshotAffectedStructs, set.create)
+  const store = transaction.doc.store
+  // check if we already split for this snapshot
+  if (!meta.has(snapshot)) {
+    snapshot.sv.forEach((clock, client) => {
+      if (clock < getState(store, client)) {
+        getItemCleanStart(transaction, createID(client, clock))
+      }
+    })
+    iterateDeletedStructs(transaction, snapshot.ds, item => {})
+    meta.add(snapshot)
+  }
+}
+
+/**
+ * @param {Doc} originDoc
+ * @param {Snapshot} snapshot
+ * @param {Doc} [newDoc] Optionally, you may define the Yjs document that receives the data from originDoc
+ * @return {Doc}
+ */
+export const createDocFromSnapshot = (originDoc, snapshot, newDoc = new Doc()) => {
+  if (originDoc.gc) {
+    // we should not try to restore a GC-ed document, because some of the restored items might have their content deleted
+    throw new Error('originDoc must not be garbage collected')
+  }
+  const { sv, ds } = snapshot
+
+  const encoder = new UpdateEncoderV2()
+  originDoc.transact(transaction => {
+    let size = 0
+    sv.forEach(clock => {
+      if (clock > 0) {
+        size++
+      }
+    })
+    encoding.writeVarUint(encoder.restEncoder, size)
+    // splitting the structs before writing them to the encoder
+    for (const [client, clock] of sv) {
+      if (clock === 0) {
+        continue
+      }
+      if (clock < getState(originDoc.store, client)) {
+        getItemCleanStart(transaction, createID(client, clock))
+      }
+      const structs = originDoc.store.clients.get(client) || []
+      const lastStructIndex = findIndexSS(structs, clock - 1)
+      // write # encoded structs
+      encoding.writeVarUint(encoder.restEncoder, lastStructIndex + 1)
+      encoder.writeClient(client)
+      // first clock written is 0
+      encoding.writeVarUint(encoder.restEncoder, 0)
+      for (let i = 0; i <= lastStructIndex; i++) {
+        structs[i].write(encoder, 0)
+      }
+    }
+    writeDeleteSet(encoder, ds)
+  })
+
+  applyUpdateV2(newDoc, encoder.toUint8Array(), 'snapshot')
+  return newDoc
+}
--- a/src/utils/StructStore.js
+++ b/src/utils/StructStore.js
@@ -0,0 +1,262 @@
+
+import {
+  GC,
+  splitItem,
+  Transaction, ID, Item, DSDecoderV2 // eslint-disable-line
+} from '../internals.js'
+
+import * as math from 'lib0/math'
+import * as error from 'lib0/error'
+
+export class StructStore {
+  constructor () {
+    /**
+     * @type {Map<number,Array<GC|Item>>}
+     */
+    this.clients = new Map()
+    /**
+     * @type {null | { missing: Map<number, number>, update: Uint8Array }}
+     */
+    this.pendingStructs = null
+    /**
+     * @type {null | Uint8Array}
+     */
+    this.pendingDs = null
+  }
+}
+
+/**
+ * Return the states as a Map<client,clock>.
+ * Note that clock refers to the next expected clock id.
+ *
+ * @param {StructStore} store
+ * @return {Map<number,number>}
+ *
+ * @public
+ * @function
+ */
+export const getStateVector = store => {
+  const sm = new Map()
+  store.clients.forEach((structs, client) => {
+    const struct = structs[structs.length - 1]
+    sm.set(client, struct.id.clock + struct.length)
+  })
+  return sm
+}
+
+/**
+ * @param {StructStore} store
+ * @param {number} client
+ * @return {number}
+ *
+ * @public
+ * @function
+ */
+export const getState = (store, client) => {
+  const structs = store.clients.get(client)
+  if (structs === undefined) {
+    return 0
+  }
+  const lastStruct = structs[structs.length - 1]
+  return lastStruct.id.clock + lastStruct.length
+}
+
+/**
+ * @param {StructStore} store
+ *
+ * @private
+ * @function
+ */
+export const integretyCheck = store => {
+  store.clients.forEach(structs => {
+    for (let i = 1; i < structs.length; i++) {
+      const l = structs[i - 1]
+      const r = structs[i]
+      if (l.id.clock + l.length !== r.id.clock) {
+        throw new Error('StructStore failed integrety check')
+      }
+    }
+  })
+}
+
+/**
+ * @param {StructStore} store
+ * @param {GC|Item} struct
+ *
+ * @private
+ * @function
+ */
+export const addStruct = (store, struct) => {
+  let structs = store.clients.get(struct.id.client)
+  if (structs === undefined) {
+    structs = []
+    store.clients.set(struct.id.client, structs)
+  } else {
+    const lastStruct = structs[structs.length - 1]
+    if (lastStruct.id.clock + lastStruct.length !== struct.id.clock) {
+      throw error.unexpectedCase()
+    }
+  }
+  structs.push(struct)
+}
+
+/**
+ * Perform a binary search on a sorted array
+ * @param {Array<Item|GC>} structs
+ * @param {number} clock
+ * @return {number}
+ *
+ * @private
+ * @function
+ */
+export const findIndexSS = (structs, clock) => {
+  let left = 0
+  let right = structs.length - 1
+  let mid = structs[right]
+  let midclock = mid.id.clock
+  if (midclock === clock) {
+    return right
+  }
+  // @todo does it even make sense to pivot the search?
+  // If a good split misses, it might actually increase the time to find the correct item.
+  // Currently, the only advantage is that search with pivoting might find the item on the first try.
+  let midindex = math.floor((clock / (midclock + mid.length - 1)) * right) // pivoting the search
+  while (left <= right) {
+    mid = structs[midindex]
+    midclock = mid.id.clock
+    if (midclock <= clock) {
+      if (clock < midclock + mid.length) {
+        return midindex
+      }
+      left = midindex + 1
+    } else {
+      right = midindex - 1
+    }
+    midindex = math.floor((left + right) / 2)
+  }
+  // Always check state before looking for a struct in StructStore
+  // Therefore the case of not finding a struct is unexpected
+  throw error.unexpectedCase()
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {GC|Item}
+ *
+ * @private
+ * @function
+ */
+export const find = (store, id) => {
+  /**
+   * @type {Array<GC|Item>}
+   */
+  // @ts-ignore
+  const structs = store.clients.get(id.client)
+  return structs[findIndexSS(structs, id.clock)]
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ * @private
+ * @function
+ */
+export const getItem = /** @type {function(StructStore,ID):Item} */ (find)
+
+/**
+ * @param {Transaction} transaction
+ * @param {Array<Item|GC>} structs
+ * @param {number} clock
+ */
+export const findIndexCleanStart = (transaction, structs, clock) => {
+  const index = findIndexSS(structs, clock)
+  const struct = structs[index]
+  if (struct.id.clock < clock && struct instanceof Item) {
+    structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock))
+    return index + 1
+  }
+  return index
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {Transaction} transaction
+ * @param {ID} id
+ * @return {Item}
+ *
+ * @private
+ * @function
+ */
+export const getItemCleanStart = (transaction, id) => {
+  const structs = /** @type {Array<Item>} */ (transaction.doc.store.clients.get(id.client))
+  return structs[findIndexCleanStart(transaction, structs, id.clock)]
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {Item}
+ *
+ * @private
+ * @function
+ */
+export const getItemCleanEnd = (transaction, store, id) => {
+  /**
+   * @type {Array<Item>}
+   */
+  // @ts-ignore
+  const structs = store.clients.get(id.client)
+  const index = findIndexSS(structs, id.clock)
+  const struct = structs[index]
+  if (id.clock !== struct.id.clock + struct.length - 1 && struct.constructor !== GC) {
+    structs.splice(index + 1, 0, splitItem(transaction, struct, id.clock - struct.id.clock + 1))
+  }
+  return struct
+}
+
+/**
+ * Replace `item` with `newitem` in store
+ * @param {StructStore} store
+ * @param {GC|Item} struct
+ * @param {GC|Item} newStruct
+ *
+ * @private
+ * @function
+ */
+export const replaceStruct = (store, struct, newStruct) => {
+  const structs = /** @type {Array<GC|Item>} */ (store.clients.get(struct.id.client))
+  structs[findIndexSS(structs, struct.id.clock)] = newStruct
+}
+
+/**
+ * Iterate over a range of structs
+ *
+ * @param {Transaction} transaction
+ * @param {Array<Item|GC>} structs
+ * @param {number} clockStart Inclusive start
+ * @param {number} len
+ * @param {function(GC|Item):void} f
+ *
+ * @function
+ */
+export const iterateStructs = (transaction, structs, clockStart, len, f) => {
+  if (len === 0) {
+    return
+  }
+  const clockEnd = clockStart + len
+  let index = findIndexCleanStart(transaction, structs, clockStart)
+  let struct
+  do {
+    struct = structs[index++]
+    if (clockEnd < struct.id.clock + struct.length) {
+      findIndexCleanStart(transaction, structs, clockEnd)
+    }
+    f(struct)
+  } while (index < structs.length && structs[index].id.clock < clockEnd)
+}
--- a/src/utils/Transaction.js
+++ b/src/utils/Transaction.js
@@ -0,0 +1,413 @@
+
+import {
+  getState,
+  writeStructsFromTransaction,
+  writeDeleteSet,
+  DeleteSet,
+  sortAndMergeDeleteSet,
+  getStateVector,
+  findIndexSS,
+  callEventHandlerListeners,
+  Item,
+  generateNewClientId,
+  createID,
+  UpdateEncoderV1, UpdateEncoderV2, GC, StructStore, AbstractType, AbstractStruct, YEvent, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as math from 'lib0/math'
+import * as set from 'lib0/set'
+import * as logging from 'lib0/logging'
+import { callAll } from 'lib0/function'
+
+/**
+ * A transaction is created for every change on the Yjs model. It is possible
+ * to bundle changes on the Yjs model in a single transaction to
+ * minimize the number on messages sent and the number of observer calls.
+ * If possible the user of this library should bundle as many changes as
+ * possible. Here is an example to illustrate the advantages of bundling:
+ *
+ * @example
+ * const map = y.define('map', YMap)
+ * // Log content when change is triggered
+ * map.observe(() => {
+ *   console.log('change triggered')
+ * })
+ * // Each change on the map type triggers a log message:
+ * map.set('a', 0) // => "change triggered"
+ * map.set('b', 0) // => "change triggered"
+ * // When put in a transaction, it will trigger the log after the transaction:
+ * y.transact(() => {
+ *   map.set('a', 1)
+ *   map.set('b', 1)
+ * }) // => "change triggered"
+ *
+ * @public
+ */
+export class Transaction {
+  /**
+   * @param {Doc} doc
+   * @param {any} origin
+   * @param {boolean} local
+   */
+  constructor (doc, origin, local) {
+    /**
+     * The Yjs instance.
+     * @type {Doc}
+     */
+    this.doc = doc
+    /**
+     * Describes the set of deleted items by ids
+     * @type {DeleteSet}
+     */
+    this.deleteSet = new DeleteSet()
+    /**
+     * Holds the state before the transaction started.
+     * @type {Map<Number,Number>}
+     */
+    this.beforeState = getStateVector(doc.store)
+    /**
+     * Holds the state after the transaction.
+     * @type {Map<Number,Number>}
+     */
+    this.afterState = new Map()
+    /**
+     * All types that were directly modified (property added or child
+     * inserted/deleted). New types are not included in this Set.
+     * Maps from type to parentSubs (`item.parentSub = null` for YArray)
+     * @type {Map<AbstractType<YEvent>,Set<String|null>>}
+     */
+    this.changed = new Map()
+    /**
+     * Stores the events for the types that observe also child elements.
+     * It is mainly used by `observeDeep`.
+     * @type {Map<AbstractType<YEvent>,Array<YEvent>>}
+     */
+    this.changedParentTypes = new Map()
+    /**
+     * @type {Array<AbstractStruct>}
+     */
+    this._mergeStructs = []
+    /**
+     * @type {any}
+     */
+    this.origin = origin
+    /**
+     * Stores meta information on the transaction
+     * @type {Map<any,any>}
+     */
+    this.meta = new Map()
+    /**
+     * Whether this change originates from this doc.
+     * @type {boolean}
+     */
+    this.local = local
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsAdded = new Set()
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsRemoved = new Set()
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsLoaded = new Set()
+  }
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Transaction} transaction
+ * @return {boolean} Whether data was written.
+ */
+export const writeUpdateMessageFromTransaction = (encoder, transaction) => {
+  if (transaction.deleteSet.clients.size === 0 && !map.any(transaction.afterState, (clock, client) => transaction.beforeState.get(client) !== clock)) {
+    return false
+  }
+  sortAndMergeDeleteSet(transaction.deleteSet)
+  writeStructsFromTransaction(encoder, transaction)
+  writeDeleteSet(encoder, transaction.deleteSet)
+  return true
+}
+
+/**
+ * @param {Transaction} transaction
+ *
+ * @private
+ * @function
+ */
+export const nextID = transaction => {
+  const y = transaction.doc
+  return createID(y.clientID, getState(y.store, y.clientID))
+}
+
+/**
+ * If `type.parent` was added in current transaction, `type` technically
+ * did not change, it was just added and we should not fire events for `type`.
+ *
+ * @param {Transaction} transaction
+ * @param {AbstractType<YEvent>} type
+ * @param {string|null} parentSub
+ */
+export const addChangedTypeToTransaction = (transaction, type, parentSub) => {
+  const item = type._item
+  if (item === null || (item.id.clock < (transaction.beforeState.get(item.id.client) || 0) && !item.deleted)) {
+    map.setIfUndefined(transaction.changed, type, set.create).add(parentSub)
+  }
+}
+
+/**
+ * @param {Array<AbstractStruct>} structs
+ * @param {number} pos
+ */
+const tryToMergeWithLeft = (structs, pos) => {
+  const left = structs[pos - 1]
+  const right = structs[pos]
+  if (left.deleted === right.deleted && left.constructor === right.constructor) {
+    if (left.mergeWith(right)) {
+      structs.splice(pos, 1)
+      if (right instanceof Item && right.parentSub !== null && /** @type {AbstractType<any>} */ (right.parent)._map.get(right.parentSub) === right) {
+        /** @type {AbstractType<any>} */ (right.parent)._map.set(right.parentSub, /** @type {Item} */ (left))
+      }
+    }
+  }
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ * @param {function(Item):boolean} gcFilter
+ */
+const tryGcDeleteSet = (ds, store, gcFilter) => {
+  for (const [client, deleteItems] of ds.clients.entries()) {
+    const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+    for (let di = deleteItems.length - 1; di >= 0; di--) {
+      const deleteItem = deleteItems[di]
+      const endDeleteItemClock = deleteItem.clock + deleteItem.len
+      for (
+        let si = findIndexSS(structs, deleteItem.clock), struct = structs[si];
+        si < structs.length && struct.id.clock < endDeleteItemClock;
+        struct = structs[++si]
+      ) {
+        const struct = structs[si]
+        if (deleteItem.clock + deleteItem.len <= struct.id.clock) {
+          break
+        }
+        if (struct instanceof Item && struct.deleted && !struct.keep && gcFilter(struct)) {
+          struct.gc(store, false)
+        }
+      }
+    }
+  }
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ */
+const tryMergeDeleteSet = (ds, store) => {
+  // try to merge deleted / gc'd items
+  // merge from right to left for better efficiecy and so we don't miss any merge targets
+  ds.clients.forEach((deleteItems, client) => {
+    const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+    for (let di = deleteItems.length - 1; di >= 0; di--) {
+      const deleteItem = deleteItems[di]
+      // start with merging the item next to the last deleted item
+      const mostRightIndexToCheck = math.min(structs.length - 1, 1 + findIndexSS(structs, deleteItem.clock + deleteItem.len - 1))
+      for (
+        let si = mostRightIndexToCheck, struct = structs[si];
+        si > 0 && struct.id.clock >= deleteItem.clock;
+        struct = structs[--si]
+      ) {
+        tryToMergeWithLeft(structs, si)
+      }
+    }
+  })
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ * @param {function(Item):boolean} gcFilter
+ */
+export const tryGc = (ds, store, gcFilter) => {
+  tryGcDeleteSet(ds, store, gcFilter)
+  tryMergeDeleteSet(ds, store)
+}
+
+/**
+ * @param {Array<Transaction>} transactionCleanups
+ * @param {number} i
+ */
+const cleanupTransactions = (transactionCleanups, i) => {
+  if (i < transactionCleanups.length) {
+    const transaction = transactionCleanups[i]
+    const doc = transaction.doc
+    const store = doc.store
+    const ds = transaction.deleteSet
+    const mergeStructs = transaction._mergeStructs
+    try {
+      sortAndMergeDeleteSet(ds)
+      transaction.afterState = getStateVector(transaction.doc.store)
+      doc._transaction = null
+      doc.emit('beforeObserverCalls', [transaction, doc])
+      /**
+       * An array of event callbacks.
+       *
+       * Each callback is called even if the other ones throw errors.
+       *
+       * @type {Array<function():void>}
+       */
+      const fs = []
+      // observe events on changed types
+      transaction.changed.forEach((subs, itemtype) =>
+        fs.push(() => {
+          if (itemtype._item === null || !itemtype._item.deleted) {
+            itemtype._callObserver(transaction, subs)
+          }
+        })
+      )
+      fs.push(() => {
+        // deep observe events
+        transaction.changedParentTypes.forEach((events, type) =>
+          fs.push(() => {
+            // We need to think about the possibility that the user transforms the
+            // Y.Doc in the event.
+            if (type._item === null || !type._item.deleted) {
+              events = events
+                .filter(event =>
+                  event.target._item === null || !event.target._item.deleted
+                )
+              events
+                .forEach(event => {
+                  event.currentTarget = type
+                })
+              // sort events by path length so that top-level events are fired first.
+              events
+                .sort((event1, event2) => event1.path.length - event2.path.length)
+              // We don't need to check for events.length
+              // because we know it has at least one element
+              callEventHandlerListeners(type._dEH, events, transaction)
+            }
+          })
+        )
+        fs.push(() => doc.emit('afterTransaction', [transaction, doc]))
+      })
+      callAll(fs, [])
+    } finally {
+      // Replace deleted items with ItemDeleted / GC.
+      // This is where content is actually remove from the Yjs Doc.
+      if (doc.gc) {
+        tryGcDeleteSet(ds, store, doc.gcFilter)
+      }
+      tryMergeDeleteSet(ds, store)
+
+      // on all affected store.clients props, try to merge
+      transaction.afterState.forEach((clock, client) => {
+        const beforeClock = transaction.beforeState.get(client) || 0
+        if (beforeClock !== clock) {
+          const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+          // we iterate from right to left so we can safely remove entries
+          const firstChangePos = math.max(findIndexSS(structs, beforeClock), 1)
+          for (let i = structs.length - 1; i >= firstChangePos; i--) {
+            tryToMergeWithLeft(structs, i)
+          }
+        }
+      })
+      // try to merge mergeStructs
+      // @todo: it makes more sense to transform mergeStructs to a DS, sort it, and merge from right to left
+      //        but at the moment DS does not handle duplicates
+      for (let i = 0; i < mergeStructs.length; i++) {
+        const { client, clock } = mergeStructs[i].id
+        const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+        const replacedStructPos = findIndexSS(structs, clock)
+        if (replacedStructPos + 1 < structs.length) {
+          tryToMergeWithLeft(structs, replacedStructPos + 1)
+        }
+        if (replacedStructPos > 0) {
+          tryToMergeWithLeft(structs, replacedStructPos)
+        }
+      }
+      if (!transaction.local && transaction.afterState.get(doc.clientID) !== transaction.beforeState.get(doc.clientID)) {
+        doc.clientID = generateNewClientId()
+        logging.print(logging.ORANGE, logging.BOLD, '[yjs] ', logging.UNBOLD, logging.RED, 'Changed the client-id because another client seems to be using it.')
+      }
+      // @todo Merge all the transactions into one and provide send the data as a single update message
+      doc.emit('afterTransactionCleanup', [transaction, doc])
+      if (doc._observers.has('update')) {
+        const encoder = new UpdateEncoderV1()
+        const hasContent = writeUpdateMessageFromTransaction(encoder, transaction)
+        if (hasContent) {
+          doc.emit('update', [encoder.toUint8Array(), transaction.origin, doc, transaction])
+        }
+      }
+      if (doc._observers.has('updateV2')) {
+        const encoder = new UpdateEncoderV2()
+        const hasContent = writeUpdateMessageFromTransaction(encoder, transaction)
+        if (hasContent) {
+          doc.emit('updateV2', [encoder.toUint8Array(), transaction.origin, doc, transaction])
+        }
+      }
+      const { subdocsAdded, subdocsLoaded, subdocsRemoved } = transaction
+      if (subdocsAdded.size > 0 || subdocsRemoved.size > 0 || subdocsLoaded.size > 0) {
+        subdocsAdded.forEach(subdoc => {
+          subdoc.clientID = doc.clientID
+          if (subdoc.collectionid == null) {
+            subdoc.collectionid = doc.collectionid
+          }
+          doc.subdocs.add(subdoc)
+        })
+        subdocsRemoved.forEach(subdoc => doc.subdocs.delete(subdoc))
+        doc.emit('subdocs', [{ loaded: subdocsLoaded, added: subdocsAdded, removed: subdocsRemoved }, doc, transaction])
+        subdocsRemoved.forEach(subdoc => subdoc.destroy())
+      }
+
+      if (transactionCleanups.length <= i + 1) {
+        doc._transactionCleanups = []
+        doc.emit('afterAllTransactions', [doc, transactionCleanups])
+      } else {
+        cleanupTransactions(transactionCleanups, i + 1)
+      }
+    }
+  }
+}
+
+/**
+ * Implements the functionality of `y.transact(()=>{..})`
+ *
+ * @param {Doc} doc
+ * @param {function(Transaction):void} f
+ * @param {any} [origin=true]
+ *
+ * @function
+ */
+export const transact = (doc, f, origin = null, local = true) => {
+  const transactionCleanups = doc._transactionCleanups
+  let initialCall = false
+  if (doc._transaction === null) {
+    initialCall = true
+    doc._transaction = new Transaction(doc, origin, local)
+    transactionCleanups.push(doc._transaction)
+    if (transactionCleanups.length === 1) {
+      doc.emit('beforeAllTransactions', [doc])
+    }
+    doc.emit('beforeTransaction', [doc._transaction, doc])
+  }
+  try {
+    f(doc._transaction)
+  } finally {
+    if (initialCall && transactionCleanups[0] === doc._transaction) {
+      // The first transaction ended, now process observer calls.
+      // Observer call may create new transactions for which we need to call the observers and do cleanup.
+      // We don't want to nest these calls, so we execute these calls one after
+      // another.
+      // Also we need to ensure that all cleanups are called, even if the
+      // observes throw errors.
+      // This file is full of hacky try {} finally {} blocks to ensure that an
+      // event can throw errors and also that the cleanup is called.
+      cleanupTransactions(transactionCleanups, 0)
+    }
+  }
+}
--- a/src/utils/UndoManager.js
+++ b/src/utils/UndoManager.js
@@ -0,0 +1,285 @@
+import {
+  mergeDeleteSets,
+  iterateDeletedStructs,
+  keepItem,
+  transact,
+  createID,
+  redoItem,
+  isParentOf,
+  followRedone,
+  getItemCleanStart,
+  isDeleted,
+  addToDeleteSet,
+  Transaction, Doc, Item, GC, DeleteSet, AbstractType, YEvent // eslint-disable-line
+} from '../internals.js'
+
+import * as time from 'lib0/time'
+import { Observable } from 'lib0/observable'
+
+class StackItem {
+  /**
+   * @param {DeleteSet} deletions
+   * @param {DeleteSet} insertions
+   */
+  constructor (deletions, insertions) {
+    this.insertions = insertions
+    this.deletions = deletions
+    /**
+     * Use this to save and restore metadata like selection range
+     */
+    this.meta = new Map()
+  }
+}
+
+/**
+ * @param {UndoManager} undoManager
+ * @param {Array<StackItem>} stack
+ * @param {string} eventType
+ * @return {StackItem?}
+ */
+const popStackItem = (undoManager, stack, eventType) => {
+  /**
+   * Whether a change happened
+   * @type {StackItem?}
+   */
+  let result = null
+  /**
+   * Keep a reference to the transaction so we can fire the event with the changedParentTypes
+   * @type {any}
+   */
+  let _tr = null
+  const doc = undoManager.doc
+  const scope = undoManager.scope
+  transact(doc, transaction => {
+    while (stack.length > 0 && result === null) {
+      const store = doc.store
+      const stackItem = /** @type {StackItem} */ (stack.pop())
+      /**
+       * @type {Set<Item>}
+       */
+      const itemsToRedo = new Set()
+      /**
+       * @type {Array<Item>}
+       */
+      const itemsToDelete = []
+      let performedChange = false
+      iterateDeletedStructs(transaction, stackItem.insertions, struct => {
+        if (struct instanceof Item) {
+          if (struct.redone !== null) {
+            let { item, diff } = followRedone(store, struct.id)
+            if (diff > 0) {
+              item = getItemCleanStart(transaction, createID(item.id.client, item.id.clock + diff))
+            }
+            struct = item
+          }
+          if (!struct.deleted && scope.some(type => isParentOf(type, /** @type {Item} */ (struct)))) {
+            itemsToDelete.push(struct)
+          }
+        }
+      })
+      iterateDeletedStructs(transaction, stackItem.deletions, struct => {
+        if (
+          struct instanceof Item &&
+          scope.some(type => isParentOf(type, struct)) &&
+          // Never redo structs in stackItem.insertions because they were created and deleted in the same capture interval.
+          !isDeleted(stackItem.insertions, struct.id)
+        ) {
+          itemsToRedo.add(struct)
+        }
+      })
+      itemsToRedo.forEach(struct => {
+        performedChange = redoItem(transaction, struct, itemsToRedo, itemsToDelete) !== null || performedChange
+      })
+      // We want to delete in reverse order so that children are deleted before
+      // parents, so we have more information available when items are filtered.
+      for (let i = itemsToDelete.length - 1; i >= 0; i--) {
+        const item = itemsToDelete[i]
+        if (undoManager.deleteFilter(item)) {
+          item.delete(transaction)
+          performedChange = true
+        }
+      }
+      result = performedChange ? stackItem : null
+    }
+    transaction.changed.forEach((subProps, type) => {
+      // destroy search marker if necessary
+      if (subProps.has(null) && type._searchMarker) {
+        type._searchMarker.length = 0
+      }
+    })
+    _tr = transaction
+  }, undoManager)
+  if (result != null) {
+    const changedParentTypes = _tr.changedParentTypes
+    undoManager.emit('stack-item-popped', [{ stackItem: result, type: eventType, changedParentTypes }, undoManager])
+  }
+  return result
+}
+
+/**
+ * @typedef {Object} UndoManagerOptions
+ * @property {number} [UndoManagerOptions.captureTimeout=500]
+ * @property {function(Item):boolean} [UndoManagerOptions.deleteFilter=()=>true] Sometimes
+ * it is necessary to filter whan an Undo/Redo operation can delete. If this
+ * filter returns false, the type/item won't be deleted even it is in the
+ * undo/redo scope.
+ * @property {Set<any>} [UndoManagerOptions.trackedOrigins=new Set([null])]
+ */
+
+/**
+ * Fires 'stack-item-added' event when a stack item was added to either the undo- or
+ * the redo-stack. You may store additional stack information via the
+ * metadata property on `event.stackItem.meta` (it is a `Map` of metadata properties).
+ * Fires 'stack-item-popped' event when a stack item was popped from either the
+ * undo- or the redo-stack. You may restore the saved stack information from `event.stackItem.meta`.
+ *
+ * @extends {Observable<'stack-item-added'|'stack-item-popped'>}
+ */
+export class UndoManager extends Observable {
+  /**
+   * @param {AbstractType<any>|Array<AbstractType<any>>} typeScope Accepts either a single type, or an array of types
+   * @param {UndoManagerOptions} options
+   */
+  constructor (typeScope, { captureTimeout = 500, deleteFilter = () => true, trackedOrigins = new Set([null]) } = {}) {
+    super()
+    this.scope = typeScope instanceof Array ? typeScope : [typeScope]
+    this.deleteFilter = deleteFilter
+    trackedOrigins.add(this)
+    this.trackedOrigins = trackedOrigins
+    /**
+     * @type {Array<StackItem>}
+     */
+    this.undoStack = []
+    /**
+     * @type {Array<StackItem>}
+     */
+    this.redoStack = []
+    /**
+     * Whether the client is currently undoing (calling UndoManager.undo)
+     *
+     * @type {boolean}
+     */
+    this.undoing = false
+    this.redoing = false
+    this.doc = /** @type {Doc} */ (this.scope[0].doc)
+    this.lastChange = 0
+    this.doc.on('afterTransaction', /** @param {Transaction} transaction */ transaction => {
+      // Only track certain transactions
+      if (!this.scope.some(type => transaction.changedParentTypes.has(type)) || (!this.trackedOrigins.has(transaction.origin) && (!transaction.origin || !this.trackedOrigins.has(transaction.origin.constructor)))) {
+        return
+      }
+      const undoing = this.undoing
+      const redoing = this.redoing
+      const stack = undoing ? this.redoStack : this.undoStack
+      if (undoing) {
+        this.stopCapturing() // next undo should not be appended to last stack item
+      } else if (!redoing) {
+        // neither undoing nor redoing: delete redoStack
+        this.redoStack = []
+      }
+      const insertions = new DeleteSet()
+      transaction.afterState.forEach((endClock, client) => {
+        const startClock = transaction.beforeState.get(client) || 0
+        const len = endClock - startClock
+        if (len > 0) {
+          addToDeleteSet(insertions, client, startClock, len)
+        }
+      })
+      const now = time.getUnixTime()
+      if (now - this.lastChange < captureTimeout && stack.length > 0 && !undoing && !redoing) {
+        // append change to last stack op
+        const lastOp = stack[stack.length - 1]
+        lastOp.deletions = mergeDeleteSets([lastOp.deletions, transaction.deleteSet])
+        lastOp.insertions = mergeDeleteSets([lastOp.insertions, insertions])
+      } else {
+        // create a new stack op
+        stack.push(new StackItem(transaction.deleteSet, insertions))
+      }
+      if (!undoing && !redoing) {
+        this.lastChange = now
+      }
+      // make sure that deleted structs are not gc'd
+      iterateDeletedStructs(transaction, transaction.deleteSet, /** @param {Item|GC} item */ item => {
+        if (item instanceof Item && this.scope.some(type => isParentOf(type, item))) {
+          keepItem(item, true)
+        }
+      })
+      this.emit('stack-item-added', [{ stackItem: stack[stack.length - 1], origin: transaction.origin, type: undoing ? 'redo' : 'undo', changedParentTypes: transaction.changedParentTypes }, this])
+    })
+  }
+
+  clear () {
+    this.doc.transact(transaction => {
+      /**
+       * @param {StackItem} stackItem
+       */
+      const clearItem = stackItem => {
+        iterateDeletedStructs(transaction, stackItem.deletions, item => {
+          if (item instanceof Item && this.scope.some(type => isParentOf(type, item))) {
+            keepItem(item, false)
+          }
+        })
+      }
+      this.undoStack.forEach(clearItem)
+      this.redoStack.forEach(clearItem)
+    })
+    this.undoStack = []
+    this.redoStack = []
+  }
+
+  /**
+   * UndoManager merges Undo-StackItem if they are created within time-gap
+   * smaller than `options.captureTimeout`. Call `um.stopCapturing()` so that the next
+   * StackItem won't be merged.
+   *
+   *
+   * @example
+   *     // without stopCapturing
+   *     ytext.insert(0, 'a')
+   *     ytext.insert(1, 'b')
+   *     um.undo()
+   *     ytext.toString() // => '' (note that 'ab' was removed)
+   *     // with stopCapturing
+   *     ytext.insert(0, 'a')
+   *     um.stopCapturing()
+   *     ytext.insert(0, 'b')
+   *     um.undo()
+   *     ytext.toString() // => 'a' (note that only 'b' was removed)
+   *
+   */
+  stopCapturing () {
+    this.lastChange = 0
+  }
+
+  /**
+   * Undo last changes on type.
+   *
+   * @return {StackItem?} Returns StackItem if a change was applied
+   */
+  undo () {
+    this.undoing = true
+    let res
+    try {
+      res = popStackItem(this, this.undoStack, 'undo')
+    } finally {
+      this.undoing = false
+    }
+    return res
+  }
+
+  /**
+   * Redo last undo operation.
+   *
+   * @return {StackItem?} Returns StackItem if a change was applied
+   */
+  redo () {
+    this.redoing = true
+    let res
+    try {
+      res = popStackItem(this, this.redoStack, 'redo')
+    } finally {
+      this.redoing = false
+    }
+    return res
+  }
+}
--- a/src/utils/UpdateDecoder.js
+++ b/src/utils/UpdateDecoder.js
@@ -0,0 +1,281 @@
+import * as buffer from 'lib0/buffer'
+import * as decoding from 'lib0/decoding'
+import {
+  ID, createID
+} from '../internals.js'
+
+export class DSDecoderV1 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    this.restDecoder = decoder
+  }
+
+  resetDsCurVal () {
+    // nop
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsClock () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsLen () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+}
+
+export class UpdateDecoderV1 extends DSDecoderV1 {
+  /**
+   * @return {ID}
+   */
+  readLeftID () {
+    return createID(decoding.readVarUint(this.restDecoder), decoding.readVarUint(this.restDecoder))
+  }
+
+  /**
+   * @return {ID}
+   */
+  readRightID () {
+    return createID(decoding.readVarUint(this.restDecoder), decoding.readVarUint(this.restDecoder))
+  }
+
+  /**
+   * Read the next client id.
+   * Use this in favor of readID whenever possible to reduce the number of objects created.
+   */
+  readClient () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readInfo () {
+    return decoding.readUint8(this.restDecoder)
+  }
+
+  /**
+   * @return {string}
+   */
+  readString () {
+    return decoding.readVarString(this.restDecoder)
+  }
+
+  /**
+   * @return {boolean} isKey
+   */
+  readParentInfo () {
+    return decoding.readVarUint(this.restDecoder) === 1
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readTypeRef () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @return {number} len
+   */
+  readLen () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {any}
+   */
+  readAny () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {Uint8Array}
+   */
+  readBuf () {
+    return buffer.copyUint8Array(decoding.readVarUint8Array(this.restDecoder))
+  }
+
+  /**
+   * Legacy implementation uses JSON parse. We use any-decoding in v2.
+   *
+   * @return {any}
+   */
+  readJSON () {
+    return JSON.parse(decoding.readVarString(this.restDecoder))
+  }
+
+  /**
+   * @return {string}
+   */
+  readKey () {
+    return decoding.readVarString(this.restDecoder)
+  }
+}
+
+export class DSDecoderV2 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    /**
+     * @private
+     */
+    this.dsCurrVal = 0
+    this.restDecoder = decoder
+  }
+
+  resetDsCurVal () {
+    this.dsCurrVal = 0
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsClock () {
+    this.dsCurrVal += decoding.readVarUint(this.restDecoder)
+    return this.dsCurrVal
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsLen () {
+    const diff = decoding.readVarUint(this.restDecoder) + 1
+    this.dsCurrVal += diff
+    return diff
+  }
+}
+
+export class UpdateDecoderV2 extends DSDecoderV2 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    super(decoder)
+    /**
+     * List of cached keys. If the keys[id] does not exist, we read a new key
+     * from stringEncoder and push it to keys.
+     *
+     * @type {Array<string>}
+     */
+    this.keys = []
+    decoding.readVarUint(decoder) // read feature flag - currently unused
+    this.keyClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.clientDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.leftClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.rightClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.infoDecoder = new decoding.RleDecoder(decoding.readVarUint8Array(decoder), decoding.readUint8)
+    this.stringDecoder = new decoding.StringDecoder(decoding.readVarUint8Array(decoder))
+    this.parentInfoDecoder = new decoding.RleDecoder(decoding.readVarUint8Array(decoder), decoding.readUint8)
+    this.typeRefDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.lenDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+  }
+
+  /**
+   * @return {ID}
+   */
+  readLeftID () {
+    return new ID(this.clientDecoder.read(), this.leftClockDecoder.read())
+  }
+
+  /**
+   * @return {ID}
+   */
+  readRightID () {
+    return new ID(this.clientDecoder.read(), this.rightClockDecoder.read())
+  }
+
+  /**
+   * Read the next client id.
+   * Use this in favor of readID whenever possible to reduce the number of objects created.
+   */
+  readClient () {
+    return this.clientDecoder.read()
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readInfo () {
+    return /** @type {number} */ (this.infoDecoder.read())
+  }
+
+  /**
+   * @return {string}
+   */
+  readString () {
+    return this.stringDecoder.read()
+  }
+
+  /**
+   * @return {boolean}
+   */
+  readParentInfo () {
+    return this.parentInfoDecoder.read() === 1
+  }
+
+  /**
+   * @return {number} An unsigned 8-bit integer
+   */
+  readTypeRef () {
+    return this.typeRefDecoder.read()
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @return {number}
+   */
+  readLen () {
+    return this.lenDecoder.read()
+  }
+
+  /**
+   * @return {any}
+   */
+  readAny () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {Uint8Array}
+   */
+  readBuf () {
+    return decoding.readVarUint8Array(this.restDecoder)
+  }
+
+  /**
+   * This is mainly here for legacy purposes.
+   *
+   * Initial we incoded objects using JSON. Now we use the much faster lib0/any-encoder. This method mainly exists for legacy purposes for the v1 encoder.
+   *
+   * @return {any}
+   */
+  readJSON () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {string}
+   */
+  readKey () {
+    const keyClock = this.keyClockDecoder.read()
+    if (keyClock < this.keys.length) {
+      return this.keys[keyClock]
+    } else {
+      const key = this.stringDecoder.read()
+      this.keys.push(key)
+      return key
+    }
+  }
+}
--- a/src/utils/UpdateEncoder.js
+++ b/src/utils/UpdateEncoder.js
@@ -0,0 +1,307 @@
+
+import * as error from 'lib0/error'
+import * as encoding from 'lib0/encoding'
+
+import {
+  ID // eslint-disable-line
+} from '../internals.js'
+
+export class DSEncoderV1 {
+  constructor () {
+    this.restEncoder = encoding.createEncoder()
+  }
+
+  toUint8Array () {
+    return encoding.toUint8Array(this.restEncoder)
+  }
+
+  resetDsCurVal () {
+    // nop
+  }
+
+  /**
+   * @param {number} clock
+   */
+  writeDsClock (clock) {
+    encoding.writeVarUint(this.restEncoder, clock)
+  }
+
+  /**
+   * @param {number} len
+   */
+  writeDsLen (len) {
+    encoding.writeVarUint(this.restEncoder, len)
+  }
+}
+
+export class UpdateEncoderV1 extends DSEncoderV1 {
+  /**
+   * @param {ID} id
+   */
+  writeLeftID (id) {
+    encoding.writeVarUint(this.restEncoder, id.client)
+    encoding.writeVarUint(this.restEncoder, id.clock)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeRightID (id) {
+    encoding.writeVarUint(this.restEncoder, id.client)
+    encoding.writeVarUint(this.restEncoder, id.clock)
+  }
+
+  /**
+   * Use writeClient and writeClock instead of writeID if possible.
+   * @param {number} client
+   */
+  writeClient (client) {
+    encoding.writeVarUint(this.restEncoder, client)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeInfo (info) {
+    encoding.writeUint8(this.restEncoder, info)
+  }
+
+  /**
+   * @param {string} s
+   */
+  writeString (s) {
+    encoding.writeVarString(this.restEncoder, s)
+  }
+
+  /**
+   * @param {boolean} isYKey
+   */
+  writeParentInfo (isYKey) {
+    encoding.writeVarUint(this.restEncoder, isYKey ? 1 : 0)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeTypeRef (info) {
+    encoding.writeVarUint(this.restEncoder, info)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @param {number} len
+   */
+  writeLen (len) {
+    encoding.writeVarUint(this.restEncoder, len)
+  }
+
+  /**
+   * @param {any} any
+   */
+  writeAny (any) {
+    encoding.writeAny(this.restEncoder, any)
+  }
+
+  /**
+   * @param {Uint8Array} buf
+   */
+  writeBuf (buf) {
+    encoding.writeVarUint8Array(this.restEncoder, buf)
+  }
+
+  /**
+   * @param {any} embed
+   */
+  writeJSON (embed) {
+    encoding.writeVarString(this.restEncoder, JSON.stringify(embed))
+  }
+
+  /**
+   * @param {string} key
+   */
+  writeKey (key) {
+    encoding.writeVarString(this.restEncoder, key)
+  }
+}
+
+export class DSEncoderV2 {
+  constructor () {
+    this.restEncoder = encoding.createEncoder() // encodes all the rest / non-optimized
+    this.dsCurrVal = 0
+  }
+
+  toUint8Array () {
+    return encoding.toUint8Array(this.restEncoder)
+  }
+
+  resetDsCurVal () {
+    this.dsCurrVal = 0
+  }
+
+  /**
+   * @param {number} clock
+   */
+  writeDsClock (clock) {
+    const diff = clock - this.dsCurrVal
+    this.dsCurrVal = clock
+    encoding.writeVarUint(this.restEncoder, diff)
+  }
+
+  /**
+   * @param {number} len
+   */
+  writeDsLen (len) {
+    if (len === 0) {
+      error.unexpectedCase()
+    }
+    encoding.writeVarUint(this.restEncoder, len - 1)
+    this.dsCurrVal += len
+  }
+}
+
+export class UpdateEncoderV2 extends DSEncoderV2 {
+  constructor () {
+    super()
+    /**
+     * @type {Map<string,number>}
+     */
+    this.keyMap = new Map()
+    /**
+     * Refers to the next uniqe key-identifier to me used.
+     * See writeKey method for more information.
+     *
+     * @type {number}
+     */
+    this.keyClock = 0
+    this.keyClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.clientEncoder = new encoding.UintOptRleEncoder()
+    this.leftClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.rightClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.infoEncoder = new encoding.RleEncoder(encoding.writeUint8)
+    this.stringEncoder = new encoding.StringEncoder()
+    this.parentInfoEncoder = new encoding.RleEncoder(encoding.writeUint8)
+    this.typeRefEncoder = new encoding.UintOptRleEncoder()
+    this.lenEncoder = new encoding.UintOptRleEncoder()
+  }
+
+  toUint8Array () {
+    const encoder = encoding.createEncoder()
+    encoding.writeVarUint(encoder, 0) // this is a feature flag that we might use in the future
+    encoding.writeVarUint8Array(encoder, this.keyClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.clientEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.leftClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.rightClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, encoding.toUint8Array(this.infoEncoder))
+    encoding.writeVarUint8Array(encoder, this.stringEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, encoding.toUint8Array(this.parentInfoEncoder))
+    encoding.writeVarUint8Array(encoder, this.typeRefEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.lenEncoder.toUint8Array())
+    // @note The rest encoder is appended! (note the missing var)
+    encoding.writeUint8Array(encoder, encoding.toUint8Array(this.restEncoder))
+    return encoding.toUint8Array(encoder)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeLeftID (id) {
+    this.clientEncoder.write(id.client)
+    this.leftClockEncoder.write(id.clock)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeRightID (id) {
+    this.clientEncoder.write(id.client)
+    this.rightClockEncoder.write(id.clock)
+  }
+
+  /**
+   * @param {number} client
+   */
+  writeClient (client) {
+    this.clientEncoder.write(client)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeInfo (info) {
+    this.infoEncoder.write(info)
+  }
+
+  /**
+   * @param {string} s
+   */
+  writeString (s) {
+    this.stringEncoder.write(s)
+  }
+
+  /**
+   * @param {boolean} isYKey
+   */
+  writeParentInfo (isYKey) {
+    this.parentInfoEncoder.write(isYKey ? 1 : 0)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeTypeRef (info) {
+    this.typeRefEncoder.write(info)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @param {number} len
+   */
+  writeLen (len) {
+    this.lenEncoder.write(len)
+  }
+
+  /**
+   * @param {any} any
+   */
+  writeAny (any) {
+    encoding.writeAny(this.restEncoder, any)
+  }
+
+  /**
+   * @param {Uint8Array} buf
+   */
+  writeBuf (buf) {
+    encoding.writeVarUint8Array(this.restEncoder, buf)
+  }
+
+  /**
+   * This is mainly here for legacy purposes.
+   *
+   * Initial we incoded objects using JSON. Now we use the much faster lib0/any-encoder. This method mainly exists for legacy purposes for the v1 encoder.
+   *
+   * @param {any} embed
+   */
+  writeJSON (embed) {
+    encoding.writeAny(this.restEncoder, embed)
+  }
+
+  /**
+   * Property keys are often reused. For example, in y-prosemirror the key `bold` might
+   * occur very often. For a 3d application, the key `position` might occur very often.
+   *
+   * We cache these keys in a Map and refer to them via a unique number.
+   *
+   * @param {string} key
+   */
+  writeKey (key) {
+    const clock = this.keyMap.get(key)
+    if (clock === undefined) {
+      this.keyClockEncoder.write(this.keyClock++)
+      this.stringEncoder.write(key)
+    } else {
+      this.keyClockEncoder.write(this.keyClock++)
+    }
+  }
+}
--- a/src/utils/YEvent.js
+++ b/src/utils/YEvent.js
@@ -0,0 +1,255 @@
+
+import {
+  isDeleted,
+  Item, AbstractType, Transaction, AbstractStruct // eslint-disable-line
+} from '../internals.js'
+
+import * as set from 'lib0/set'
+import * as array from 'lib0/array'
+
+/**
+ * YEvent describes the changes on a YType.
+ */
+export class YEvent {
+  /**
+   * @param {AbstractType<any>} target The changed type.
+   * @param {Transaction} transaction
+   */
+  constructor (target, transaction) {
+    /**
+     * The type on which this event was created on.
+     * @type {AbstractType<any>}
+     */
+    this.target = target
+    /**
+     * The current target on which the observe callback is called.
+     * @type {AbstractType<any>}
+     */
+    this.currentTarget = target
+    /**
+     * The transaction that triggered this event.
+     * @type {Transaction}
+     */
+    this.transaction = transaction
+    /**
+     * @type {Object|null}
+     */
+    this._changes = null
+    /**
+     * @type {null | Map<string, { action: 'add' | 'update' | 'delete', oldValue: any, newValue: any }>}
+     */
+    this._keys = null
+    /**
+     * @type {null | Array<{ insert?: string | Array<any> | object | AbstractType<any>, retain?: number, delete?: number, attributes?: Object<string, any> }>}
+     */
+    this._delta = null
+  }
+
+  /**
+   * Computes the path from `y` to the changed type.
+   *
+   * @todo v14 should standardize on path: Array<{parent, index}> because that is easier to work with.
+   *
+   * The following property holds:
+   * @example
+   *   let type = y
+   *   event.path.forEach(dir => {
+   *     type = type.get(dir)
+   *   })
+   *   type === event.target // => true
+   */
+  get path () {
+    // @ts-ignore _item is defined because target is integrated
+    return getPathTo(this.currentTarget, this.target)
+  }
+
+  /**
+   * Check if a struct is deleted by this event.
+   *
+   * In contrast to change.deleted, this method also returns true if the struct was added and then deleted.
+   *
+   * @param {AbstractStruct} struct
+   * @return {boolean}
+   */
+  deletes (struct) {
+    return isDeleted(this.transaction.deleteSet, struct.id)
+  }
+
+  /**
+   * @type {Map<string, { action: 'add' | 'update' | 'delete', oldValue: any, newValue: any }>}
+   */
+  get keys () {
+    if (this._keys === null) {
+      const keys = new Map()
+      const target = this.target
+      const changed = /** @type Set<string|null> */ (this.transaction.changed.get(target))
+      changed.forEach(key => {
+        if (key !== null) {
+          const item = /** @type {Item} */ (target._map.get(key))
+          /**
+           * @type {'delete' | 'add' | 'update'}
+           */
+          let action
+          let oldValue
+          if (this.adds(item)) {
+            let prev = item.left
+            while (prev !== null && this.adds(prev)) {
+              prev = prev.left
+            }
+            if (this.deletes(item)) {
+              if (prev !== null && this.deletes(prev)) {
+                action = 'delete'
+                oldValue = array.last(prev.content.getContent())
+              } else {
+                return
+              }
+            } else {
+              if (prev !== null && this.deletes(prev)) {
+                action = 'update'
+                oldValue = array.last(prev.content.getContent())
+              } else {
+                action = 'add'
+                oldValue = undefined
+              }
+            }
+          } else {
+            if (this.deletes(item)) {
+              action = 'delete'
+              oldValue = array.last(/** @type {Item} */ item.content.getContent())
+            } else {
+              return // nop
+            }
+          }
+          keys.set(key, { action, oldValue })
+        }
+      })
+      this._keys = keys
+    }
+    return this._keys
+  }
+
+  /**
+   * @type {Array<{insert?: string | Array<any> | object | AbstractType<any>, retain?: number, delete?: number, attributes?: Object<string, any>}>}
+   */
+  get delta () {
+    return this.changes.delta
+  }
+
+  /**
+   * Check if a struct is added by this event.
+   *
+   * In contrast to change.deleted, this method also returns true if the struct was added and then deleted.
+   *
+   * @param {AbstractStruct} struct
+   * @return {boolean}
+   */
+  adds (struct) {
+    return struct.id.clock >= (this.transaction.beforeState.get(struct.id.client) || 0)
+  }
+
+  /**
+   * @type {{added:Set<Item>,deleted:Set<Item>,keys:Map<string,{action:'add'|'update'|'delete',oldValue:any}>,delta:Array<{insert?:Array<any>|string, delete?:number, retain?:number}>}}
+   */
+  get changes () {
+    let changes = this._changes
+    if (changes === null) {
+      const target = this.target
+      const added = set.create()
+      const deleted = set.create()
+      /**
+       * @type {Array<{insert:Array<any>}|{delete:number}|{retain:number}>}
+       */
+      const delta = []
+      changes = {
+        added,
+        deleted,
+        delta,
+        keys: this.keys
+      }
+      const changed = /** @type Set<string|null> */ (this.transaction.changed.get(target))
+      if (changed.has(null)) {
+        /**
+         * @type {any}
+         */
+        let lastOp = null
+        const packOp = () => {
+          if (lastOp) {
+            delta.push(lastOp)
+          }
+        }
+        for (let item = target._start; item !== null; item = item.right) {
+          if (item.deleted) {
+            if (this.deletes(item) && !this.adds(item)) {
+              if (lastOp === null || lastOp.delete === undefined) {
+                packOp()
+                lastOp = { delete: 0 }
+              }
+              lastOp.delete += item.length
+              deleted.add(item)
+            } // else nop
+          } else {
+            if (this.adds(item)) {
+              if (lastOp === null || lastOp.insert === undefined) {
+                packOp()
+                lastOp = { insert: [] }
+              }
+              lastOp.insert = lastOp.insert.concat(item.content.getContent())
+              added.add(item)
+            } else {
+              if (lastOp === null || lastOp.retain === undefined) {
+                packOp()
+                lastOp = { retain: 0 }
+              }
+              lastOp.retain += item.length
+            }
+          }
+        }
+        if (lastOp !== null && lastOp.retain === undefined) {
+          packOp()
+        }
+      }
+      this._changes = changes
+    }
+    return /** @type {any} */ (changes)
+  }
+}
+
+/**
+ * Compute the path from this type to the specified target.
+ *
+ * @example
+ *   // `child` should be accessible via `type.get(path[0]).get(path[1])..`
+ *   const path = type.getPathTo(child)
+ *   // assuming `type instanceof YArray`
+ *   console.log(path) // might look like => [2, 'key1']
+ *   child === type.get(path[0]).get(path[1])
+ *
+ * @param {AbstractType<any>} parent
+ * @param {AbstractType<any>} child target
+ * @return {Array<string|number>} Path to the target
+ *
+ * @private
+ * @function
+ */
+const getPathTo = (parent, child) => {
+  const path = []
+  while (child._item !== null && child !== parent) {
+    if (child._item.parentSub !== null) {
+      // parent is map-ish
+      path.unshift(child._item.parentSub)
+    } else {
+      // parent is array-ish
+      let i = 0
+      let c = /** @type {AbstractType<any>} */ (child._item.parent)._start
+      while (c !== child._item && c !== null) {
+        if (!c.deleted) {
+          i++
+        }
+        c = c.right
+      }
+      path.unshift(i)
+    }
+    child = /** @type {AbstractType<any>} */ (child._item.parent)
+  }
+  return path
+}
--- a/src/utils/encoding.js
+++ b/src/utils/encoding.js
@@ -0,0 +1,645 @@
+
+/**
+ * @module encoding
+ */
+/*
+ * We use the first five bits in the info flag for determining the type of the struct.
+ *
+ * 0: GC
+ * 1: Item with Deleted content
+ * 2: Item with JSON content
+ * 3: Item with Binary content
+ * 4: Item with String content
+ * 5: Item with Embed content (for richtext content)
+ * 6: Item with Format content (a formatting marker for richtext content)
+ * 7: Item with Type
+ */
+
+import {
+  findIndexSS,
+  getState,
+  createID,
+  getStateVector,
+  readAndApplyDeleteSet,
+  writeDeleteSet,
+  createDeleteSetFromStructStore,
+  transact,
+  readItemContent,
+  UpdateDecoderV1,
+  UpdateDecoderV2,
+  UpdateEncoderV1,
+  UpdateEncoderV2,
+  DSEncoderV2,
+  DSDecoderV1,
+  DSEncoderV1,
+  mergeUpdates,
+  mergeUpdatesV2,
+  Skip,
+  diffUpdateV2,
+  convertUpdateFormatV2ToV1,
+  DSDecoderV2, Doc, Transaction, GC, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as binary from 'lib0/binary'
+import * as map from 'lib0/map'
+import * as math from 'lib0/math'
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Array<GC|Item>} structs All structs by `client`
+ * @param {number} client
+ * @param {number} clock write structs starting with `ID(client,clock)`
+ *
+ * @function
+ */
+const writeStructs = (encoder, structs, client, clock) => {
+  // write first id
+  clock = math.max(clock, structs[0].id.clock) // make sure the first id exists
+  const startNewStructs = findIndexSS(structs, clock)
+  // write # encoded structs
+  encoding.writeVarUint(encoder.restEncoder, structs.length - startNewStructs)
+  encoder.writeClient(client)
+  encoding.writeVarUint(encoder.restEncoder, clock)
+  const firstStruct = structs[startNewStructs]
+  // write first struct with an offset
+  firstStruct.write(encoder, clock - firstStruct.id.clock)
+  for (let i = startNewStructs + 1; i < structs.length; i++) {
+    structs[i].write(encoder, 0)
+  }
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {StructStore} store
+ * @param {Map<number,number>} _sm
+ *
+ * @private
+ * @function
+ */
+export const writeClientsStructs = (encoder, store, _sm) => {
+  // we filter all valid _sm entries into sm
+  const sm = new Map()
+  _sm.forEach((clock, client) => {
+    // only write if new structs are available
+    if (getState(store, client) > clock) {
+      sm.set(client, clock)
+    }
+  })
+  getStateVector(store).forEach((clock, client) => {
+    if (!_sm.has(client)) {
+      sm.set(client, 0)
+    }
+  })
+  // write # states that were updated
+  encoding.writeVarUint(encoder.restEncoder, sm.size)
+  // Write items with higher client ids first
+  // This heavily improves the conflict algorithm.
+  Array.from(sm.entries()).sort((a, b) => b[0] - a[0]).forEach(([client, clock]) => {
+    // @ts-ignore
+    writeStructs(encoder, store.clients.get(client), client, clock)
+  })
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder The decoder object to read data from.
+ * @param {Doc} doc
+ * @return {Map<number, { i: number, refs: Array<Item | GC> }>}
+ *
+ * @private
+ * @function
+ */
+export const readClientsStructRefs = (decoder, doc) => {
+  /**
+   * @type {Map<number, { i: number, refs: Array<Item | GC> }>}
+   */
+  const clientRefs = map.create()
+  const numOfStateUpdates = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numOfStateUpdates; i++) {
+    const numberOfStructs = decoding.readVarUint(decoder.restDecoder)
+    /**
+     * @type {Array<GC|Item>}
+     */
+    const refs = new Array(numberOfStructs)
+    const client = decoder.readClient()
+    let clock = decoding.readVarUint(decoder.restDecoder)
+    // const start = performance.now()
+    clientRefs.set(client, { i: 0, refs })
+    for (let i = 0; i < numberOfStructs; i++) {
+      const info = decoder.readInfo()
+      switch (binary.BITS5 & info) {
+        case 0: { // GC
+          const len = decoder.readLen()
+          refs[i] = new GC(createID(client, clock), len)
+          clock += len
+          break
+        }
+        case 10: { // Skip Struct (nothing to apply)
+          // @todo we could reduce the amount of checks by adding Skip struct to clientRefs so we know that something is missing.
+          const len = decoding.readVarUint(decoder.restDecoder)
+          refs[i] = new Skip(createID(client, clock), len)
+          clock += len
+          break
+        }
+        default: { // Item with content
+          /**
+           * The optimized implementation doesn't use any variables because inlining variables is faster.
+           * Below a non-optimized version is shown that implements the basic algorithm with
+           * a few comments
+           */
+          const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+          // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+          // and we read the next string as parentYKey.
+          // It indicates how we store/retrieve parent from `y.share`
+          // @type {string|null}
+          const struct = new Item(
+            createID(client, clock),
+            null, // leftd
+            (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null, // origin
+            null, // right
+            (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null, // right origin
+            cantCopyParentInfo ? (decoder.readParentInfo() ? doc.get(decoder.readString()) : decoder.readLeftID()) : null, // parent
+            cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+            readItemContent(decoder, info) // item content
+          )
+          /* A non-optimized implementation of the above algorithm:
+
+          // The item that was originally to the left of this item.
+          const origin = (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null
+          // The item that was originally to the right of this item.
+          const rightOrigin = (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null
+          const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+          const hasParentYKey = cantCopyParentInfo ? decoder.readParentInfo() : false
+          // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+          // and we read the next string as parentYKey.
+          // It indicates how we store/retrieve parent from `y.share`
+          // @type {string|null}
+          const parentYKey = cantCopyParentInfo && hasParentYKey ? decoder.readString() : null
+
+          const struct = new Item(
+            createID(client, clock),
+            null, // leftd
+            origin, // origin
+            null, // right
+            rightOrigin, // right origin
+            cantCopyParentInfo && !hasParentYKey ? decoder.readLeftID() : (parentYKey !== null ? doc.get(parentYKey) : null), // parent
+            cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+            readItemContent(decoder, info) // item content
+          )
+          */
+          refs[i] = struct
+          clock += struct.length
+        }
+      }
+    }
+    // console.log('time to read: ', performance.now() - start) // @todo remove
+  }
+  return clientRefs
+}
+
+/**
+ * Resume computing structs generated by struct readers.
+ *
+ * While there is something to do, we integrate structs in this order
+ * 1. top element on stack, if stack is not empty
+ * 2. next element from current struct reader (if empty, use next struct reader)
+ *
+ * If struct causally depends on another struct (ref.missing), we put next reader of
+ * `ref.id.client` on top of stack.
+ *
+ * At some point we find a struct that has no causal dependencies,
+ * then we start emptying the stack.
+ *
+ * It is not possible to have circles: i.e. struct1 (from client1) depends on struct2 (from client2)
+ * depends on struct3 (from client1). Therefore the max stack size is eqaul to `structReaders.length`.
+ *
+ * This method is implemented in a way so that we can resume computation if this update
+ * causally depends on another update.
+ *
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @param {Map<number, { i: number, refs: (GC | Item)[] }>} clientsStructRefs
+ * @return { null | { update: Uint8Array, missing: Map<number,number> } }
+ *
+ * @private
+ * @function
+ */
+const integrateStructs = (transaction, store, clientsStructRefs) => {
+  /**
+   * @type {Array<Item | GC>}
+   */
+  const stack = []
+  // sort them so that we take the higher id first, in case of conflicts the lower id will probably not conflict with the id from the higher user.
+  let clientsStructRefsIds = Array.from(clientsStructRefs.keys()).sort((a, b) => a - b)
+  if (clientsStructRefsIds.length === 0) {
+    return null
+  }
+  const getNextStructTarget = () => {
+    if (clientsStructRefsIds.length === 0) {
+      return null
+    }
+    let nextStructsTarget = /** @type {{i:number,refs:Array<GC|Item>}} */ (clientsStructRefs.get(clientsStructRefsIds[clientsStructRefsIds.length - 1]))
+    while (nextStructsTarget.refs.length === nextStructsTarget.i) {
+      clientsStructRefsIds.pop()
+      if (clientsStructRefsIds.length > 0) {
+        nextStructsTarget = /** @type {{i:number,refs:Array<GC|Item>}} */ (clientsStructRefs.get(clientsStructRefsIds[clientsStructRefsIds.length - 1]))
+      } else {
+        return null
+      }
+    }
+    return nextStructsTarget
+  }
+  let curStructsTarget = getNextStructTarget()
+  if (curStructsTarget === null && stack.length === 0) {
+    return null
+  }
+
+  /**
+   * @type {StructStore}
+   */
+  const restStructs = new StructStore()
+  const missingSV = new Map()
+  /**
+   * @param {number} client
+   * @param {number} clock
+   */
+  const updateMissingSv = (client, clock) => {
+    const mclock = missingSV.get(client)
+    if (mclock == null || mclock > clock) {
+      missingSV.set(client, clock)
+    }
+  }
+  /**
+   * @type {GC|Item}
+   */
+  let stackHead = /** @type {any} */ (curStructsTarget).refs[/** @type {any} */ (curStructsTarget).i++]
+  // caching the state because it is used very often
+  const state = new Map()
+
+  const addStackToRestSS = () => {
+    for (const item of stack) {
+      const client = item.id.client
+      const unapplicableItems = clientsStructRefs.get(client)
+      if (unapplicableItems) {
+        // decrement because we weren't able to apply previous operation
+        unapplicableItems.i--
+        restStructs.clients.set(client, unapplicableItems.refs.slice(unapplicableItems.i))
+        clientsStructRefs.delete(client)
+        unapplicableItems.i = 0
+        unapplicableItems.refs = []
+      } else {
+        // item was the last item on clientsStructRefs and the field was already cleared. Add item to restStructs and continue
+        restStructs.clients.set(client, [item])
+      }
+      // remove client from clientsStructRefsIds to prevent users from applying the same update again
+      clientsStructRefsIds = clientsStructRefsIds.filter(c => c !== client)
+    }
+    stack.length = 0
+  }
+
+  // iterate over all struct readers until we are done
+  while (true) {
+    if (stackHead.constructor !== Skip) {
+      const localClock = map.setIfUndefined(state, stackHead.id.client, () => getState(store, stackHead.id.client))
+      const offset = localClock - stackHead.id.clock
+      if (offset < 0) {
+        // update from the same client is missing
+        stack.push(stackHead)
+        updateMissingSv(stackHead.id.client, stackHead.id.clock - 1)
+        // hid a dead wall, add all items from stack to restSS
+        addStackToRestSS()
+      } else {
+        const missing = stackHead.getMissing(transaction, store)
+        if (missing !== null) {
+          stack.push(stackHead)
+          // get the struct reader that has the missing struct
+          /**
+           * @type {{ refs: Array<GC|Item>, i: number }}
+           */
+          const structRefs = clientsStructRefs.get(/** @type {number} */ (missing)) || { refs: [], i: 0 }
+          if (structRefs.refs.length === structRefs.i) {
+            // This update message causally depends on another update message that doesn't exist yet
+            updateMissingSv(/** @type {number} */ (missing), getState(store, missing))
+            addStackToRestSS()
+          } else {
+            stackHead = structRefs.refs[structRefs.i++]
+            continue
+          }
+        } else if (offset === 0 || offset < stackHead.length) {
+          // all fine, apply the stackhead
+          stackHead.integrate(transaction, offset)
+          state.set(stackHead.id.client, stackHead.id.clock + stackHead.length)
+        }
+      }
+    }
+    // iterate to next stackHead
+    if (stack.length > 0) {
+      stackHead = /** @type {GC|Item} */ (stack.pop())
+    } else if (curStructsTarget !== null && curStructsTarget.i < curStructsTarget.refs.length) {
+      stackHead = /** @type {GC|Item} */ (curStructsTarget.refs[curStructsTarget.i++])
+    } else {
+      curStructsTarget = getNextStructTarget()
+      if (curStructsTarget === null) {
+        // we are done!
+        break
+      } else {
+        stackHead = /** @type {GC|Item} */ (curStructsTarget.refs[curStructsTarget.i++])
+      }
+    }
+  }
+  if (restStructs.clients.size > 0) {
+    const encoder = new UpdateEncoderV2()
+    writeClientsStructs(encoder, restStructs, new Map())
+    // write empty deleteset
+    // writeDeleteSet(encoder, new DeleteSet())
+    encoding.writeVarUint(encoder.restEncoder, 0) // => no need for an extra function call, just write 0 deletes
+    return { missing: missingSV, update: encoder.toUint8Array() }
+  }
+  return null
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Transaction} transaction
+ *
+ * @private
+ * @function
+ */
+export const writeStructsFromTransaction = (encoder, transaction) => writeClientsStructs(encoder, transaction.doc.store, transaction.beforeState)
+
+/**
+ * Read and apply a document update.
+ *
+ * This function has the same effect as `applyUpdate` but accepts an decoder.
+ *
+ * @param {decoding.Decoder} decoder
+ * @param {Doc} ydoc
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} [structDecoder]
+ *
+ * @function
+ */
+export const readUpdateV2 = (decoder, ydoc, transactionOrigin, structDecoder = new UpdateDecoderV2(decoder)) =>
+  transact(ydoc, transaction => {
+    // force that transaction.local is set to non-local
+    transaction.local = false
+    let retry = false
+    const doc = transaction.doc
+    const store = doc.store
+    // let start = performance.now()
+    const ss = readClientsStructRefs(structDecoder, doc)
+    // console.log('time to read structs: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    // console.log('time to merge: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    const restStructs = integrateStructs(transaction, store, ss)
+    const pending = store.pendingStructs
+    if (pending) {
+      // check if we can apply something
+      for (const [client, clock] of pending.missing) {
+        if (clock < getState(store, client)) {
+          retry = true
+          break
+        }
+      }
+      if (restStructs) {
+        // merge restStructs into store.pending
+        for (const [client, clock] of restStructs.missing) {
+          const mclock = pending.missing.get(client)
+          if (mclock == null || mclock > clock) {
+            pending.missing.set(client, clock)
+          }
+        }
+        pending.update = mergeUpdatesV2([pending.update, restStructs.update])
+      }
+    } else {
+      store.pendingStructs = restStructs
+    }
+    // console.log('time to integrate: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    const dsRest = readAndApplyDeleteSet(structDecoder, transaction, store)
+    if (store.pendingDs) {
+      // @todo we could make a lower-bound state-vector check as we do above
+      const pendingDSUpdate = new UpdateDecoderV2(decoding.createDecoder(store.pendingDs))
+      decoding.readVarUint(pendingDSUpdate.restDecoder) // read 0 structs, because we only encode deletes in pendingdsupdate
+      const dsRest2 = readAndApplyDeleteSet(pendingDSUpdate, transaction, store)
+      if (dsRest && dsRest2) {
+        // case 1: ds1 != null && ds2 != null
+        store.pendingDs = mergeUpdatesV2([dsRest, dsRest2])
+      } else {
+        // case 2: ds1 != null
+        // case 3: ds2 != null
+        // case 4: ds1 == null && ds2 == null
+        store.pendingDs = dsRest || dsRest2
+      }
+    } else {
+      // Either dsRest == null && pendingDs == null OR dsRest != null
+      store.pendingDs = dsRest
+    }
+    // console.log('time to cleanup: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+
+    // console.log('time to resume delete readers: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    if (retry) {
+      const update = /** @type {{update: Uint8Array}} */ (store.pendingStructs).update
+      store.pendingStructs = null
+      applyUpdateV2(transaction.doc, update)
+    }
+  }, transactionOrigin, false)
+
+/**
+ * Read and apply a document update.
+ *
+ * This function has the same effect as `applyUpdate` but accepts an decoder.
+ *
+ * @param {decoding.Decoder} decoder
+ * @param {Doc} ydoc
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ *
+ * @function
+ */
+export const readUpdate = (decoder, ydoc, transactionOrigin) => readUpdateV2(decoder, ydoc, transactionOrigin, new UpdateDecoderV1(decoder))
+
+/**
+ * Apply a document update created by, for example, `y.on('update', update => ..)` or `update = encodeStateAsUpdate()`.
+ *
+ * This function has the same effect as `readUpdate` but accepts an Uint8Array instead of a Decoder.
+ *
+ * @param {Doc} ydoc
+ * @param {Uint8Array} update
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ *
+ * @function
+ */
+export const applyUpdateV2 = (ydoc, update, transactionOrigin, YDecoder = UpdateDecoderV2) => {
+  const decoder = decoding.createDecoder(update)
+  readUpdateV2(decoder, ydoc, transactionOrigin, new YDecoder(decoder))
+}
+
+/**
+ * Apply a document update created by, for example, `y.on('update', update => ..)` or `update = encodeStateAsUpdate()`.
+ *
+ * This function has the same effect as `readUpdate` but accepts an Uint8Array instead of a Decoder.
+ *
+ * @param {Doc} ydoc
+ * @param {Uint8Array} update
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ *
+ * @function
+ */
+export const applyUpdate = (ydoc, update, transactionOrigin) => applyUpdateV2(ydoc, update, transactionOrigin, UpdateDecoderV1)
+
+/**
+ * Write all the document as a single update message. If you specify the state of the remote client (`targetStateVector`) it will
+ * only write the operations that are missing.
+ *
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Doc} doc
+ * @param {Map<number,number>} [targetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ *
+ * @function
+ */
+export const writeStateAsUpdate = (encoder, doc, targetStateVector = new Map()) => {
+  writeClientsStructs(encoder, doc.store, targetStateVector)
+  writeDeleteSet(encoder, createDeleteSetFromStructStore(doc.store))
+}
+
+/**
+ * Write all the document as a single update message that can be applied on the remote document. If you specify the state of the remote client (`targetState`) it will
+ * only write the operations that are missing.
+ *
+ * Use `writeStateAsUpdate` instead if you are working with lib0/encoding.js#Encoder
+ *
+ * @param {Doc} doc
+ * @param {Uint8Array} [encodedTargetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} [encoder]
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateAsUpdateV2 = (doc, encodedTargetStateVector = new Uint8Array([0]), encoder = new UpdateEncoderV2()) => {
+  const targetStateVector = decodeStateVector(encodedTargetStateVector)
+  writeStateAsUpdate(encoder, doc, targetStateVector)
+  const updates = [encoder.toUint8Array()]
+  // also add the pending updates (if there are any)
+  if (doc.store.pendingDs) {
+    updates.push(doc.store.pendingDs)
+  }
+  if (doc.store.pendingStructs) {
+    updates.push(diffUpdateV2(doc.store.pendingStructs.update, encodedTargetStateVector))
+  }
+  if (updates.length > 1) {
+    if (encoder.constructor === UpdateEncoderV1) {
+      return mergeUpdates(updates.map((update, i) => i === 0 ? update : convertUpdateFormatV2ToV1(update)))
+    } else if (encoder.constructor === UpdateEncoderV2) {
+      return mergeUpdatesV2(updates)
+    }
+  }
+  return updates[0]
+}
+
+/**
+ * Write all the document as a single update message that can be applied on the remote document. If you specify the state of the remote client (`targetState`) it will
+ * only write the operations that are missing.
+ *
+ * Use `writeStateAsUpdate` instead if you are working with lib0/encoding.js#Encoder
+ *
+ * @param {Doc} doc
+ * @param {Uint8Array} [encodedTargetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateAsUpdate = (doc, encodedTargetStateVector) => encodeStateAsUpdateV2(doc, encodedTargetStateVector, new UpdateEncoderV1())
+
+/**
+ * Read state vector from Decoder and return as Map
+ *
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+export const readStateVector = decoder => {
+  const ss = new Map()
+  const ssLength = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < ssLength; i++) {
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const clock = decoding.readVarUint(decoder.restDecoder)
+    ss.set(client, clock)
+  }
+  return ss
+}
+
+/**
+ * Read decodedState and return State as Map.
+ *
+ * @param {Uint8Array} decodedState
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+// export const decodeStateVectorV2 = decodedState => readStateVector(new DSDecoderV2(decoding.createDecoder(decodedState)))
+
+/**
+ * Read decodedState and return State as Map.
+ *
+ * @param {Uint8Array} decodedState
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+export const decodeStateVector = decodedState => readStateVector(new DSDecoderV1(decoding.createDecoder(decodedState)))
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {Map<number,number>} sv
+ * @function
+ */
+export const writeStateVector = (encoder, sv) => {
+  encoding.writeVarUint(encoder.restEncoder, sv.size)
+  sv.forEach((clock, client) => {
+    encoding.writeVarUint(encoder.restEncoder, client) // @todo use a special client decoder that is based on mapping
+    encoding.writeVarUint(encoder.restEncoder, clock)
+  })
+  return encoder
+}
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {Doc} doc
+ *
+ * @function
+ */
+export const writeDocumentStateVector = (encoder, doc) => writeStateVector(encoder, getStateVector(doc.store))
+
+/**
+ * Encode State as Uint8Array.
+ *
+ * @param {Doc|Map<number,number>} doc
+ * @param {DSEncoderV1 | DSEncoderV2} [encoder]
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateVectorV2 = (doc, encoder = new DSEncoderV2()) => {
+  if (doc instanceof Map) {
+    writeStateVector(encoder, doc)
+  } else {
+    writeDocumentStateVector(encoder, doc)
+  }
+  return encoder.toUint8Array()
+}
+
+/**
+ * Encode State as Uint8Array.
+ *
+ * @param {Doc|Map<number,number>} doc
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateVector = doc => encodeStateVectorV2(doc, new DSEncoderV1())
--- a/src/utils/isParentOf.js
+++ b/src/utils/isParentOf.js
@@ -0,0 +1,22 @@
+
+import { AbstractType, Item } from '../internals.js' // eslint-disable-line
+
+/**
+ * Check if `parent` is a parent of `child`.
+ *
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} child
+ * @return {Boolean} Whether `parent` is a parent of `child`.
+ *
+ * @private
+ * @function
+ */
+export const isParentOf = (parent, child) => {
+  while (child !== null) {
+    if (child.parent === parent) {
+      return true
+    }
+    child = /** @type {AbstractType<any>} */ (child.parent)._item
+  }
+  return false
+}
--- a/src/utils/logging.js
+++ b/src/utils/logging.js
@@ -0,0 +1,22 @@
+
+import {
+  AbstractType // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * Convenient helper to log type information.
+ *
+ * Do not use in productive systems as the output can be immense!
+ *
+ * @param {AbstractType<any>} type
+ */
+export const logType = type => {
+  const res = []
+  let n = type._start
+  while (n) {
+    res.push(n)
+    n = n.right
+  }
+  console.log('Children: ', res)
+  console.log('Children content: ', res.filter(m => !m.deleted).map(m => m.content))
+}
--- a/src/utils/updates.js
+++ b/src/utils/updates.js
@@ -0,0 +1,557 @@
+
+import * as binary from 'lib0/binary'
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+import * as logging from 'lib0/logging'
+import * as math from 'lib0/math'
+import {
+  createID,
+  readItemContent,
+  readDeleteSet,
+  writeDeleteSet,
+  Skip,
+  mergeDeleteSets,
+  DSEncoderV1,
+  DSEncoderV2,
+  decodeStateVector,
+  Item, GC, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2 // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ */
+function * lazyStructReaderGenerator (decoder) {
+  const numOfStateUpdates = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numOfStateUpdates; i++) {
+    const numberOfStructs = decoding.readVarUint(decoder.restDecoder)
+    const client = decoder.readClient()
+    let clock = decoding.readVarUint(decoder.restDecoder)
+    for (let i = 0; i < numberOfStructs; i++) {
+      const info = decoder.readInfo()
+      // @todo use switch instead of ifs
+      if (info === 10) {
+        const len = decoding.readVarUint(decoder.restDecoder)
+        yield new Skip(createID(client, clock), len)
+        clock += len
+      } else if ((binary.BITS5 & info) !== 0) {
+        const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+        // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+        // and we read the next string as parentYKey.
+        // It indicates how we store/retrieve parent from `y.share`
+        // @type {string|null}
+        const struct = new Item(
+          createID(client, clock),
+          null, // left
+          (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null, // origin
+          null, // right
+          (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null, // right origin
+          // @ts-ignore Force writing a string here.
+          cantCopyParentInfo ? (decoder.readParentInfo() ? decoder.readString() : decoder.readLeftID()) : null, // parent
+          cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+          readItemContent(decoder, info) // item content
+        )
+        yield struct
+        clock += struct.length
+      } else {
+        const len = decoder.readLen()
+        yield new GC(createID(client, clock), len)
+        clock += len
+      }
+    }
+  }
+}
+
+export class LazyStructReader {
+  /**
+   * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+   * @param {boolean} filterSkips
+   */
+  constructor (decoder, filterSkips) {
+    this.gen = lazyStructReaderGenerator(decoder)
+    /**
+     * @type {null | Item | Skip | GC}
+     */
+    this.curr = null
+    this.done = false
+    this.filterSkips = filterSkips
+    this.next()
+  }
+
+  /**
+   * @return {Item | GC | Skip |null}
+   */
+  next () {
+    // ignore "Skip" structs
+    do {
+      this.curr = this.gen.next().value || null
+    } while (this.filterSkips && this.curr !== null && this.curr.constructor === Skip)
+    return this.curr
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ *
+ */
+export const logUpdate = update => logUpdateV2(update, UpdateDecoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} [YDecoder]
+ *
+ */
+export const logUpdateV2 = (update, YDecoder = UpdateDecoderV2) => {
+  const structs = []
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    structs.push(curr)
+  }
+  logging.print('Structs: ', structs)
+  const ds = readDeleteSet(updateDecoder)
+  logging.print('DeleteSet: ', ds)
+}
+
+export class LazyStructWriter {
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  constructor (encoder) {
+    this.currClient = 0
+    this.startClock = 0
+    this.written = 0
+    this.encoder = encoder
+    /**
+     * We want to write operations lazily, but also we need to know beforehand how many operations we want to write for each client.
+     *
+     * This kind of meta-information (#clients, #structs-per-client-written) is written to the restEncoder.
+     *
+     * We fragment the restEncoder and store a slice of it per-client until we know how many clients there are.
+     * When we flush (toUint8Array) we write the restEncoder using the fragments and the meta-information.
+     *
+     * @type {Array<{ written: number, restEncoder: Uint8Array }>}
+     */
+    this.clientStructs = []
+  }
+}
+
+/**
+ * @param {Array<Uint8Array>} updates
+ * @return {Uint8Array}
+ */
+export const mergeUpdates = updates => mergeUpdatesV2(updates, UpdateDecoderV1, UpdateEncoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof DSEncoderV1 | typeof DSEncoderV2} YEncoder
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} YDecoder
+ * @return {Uint8Array}
+ */
+export const encodeStateVectorFromUpdateV2 = (update, YEncoder = DSEncoderV2, YDecoder = UpdateDecoderV2) => {
+  const encoder = new YEncoder()
+  const updateDecoder = new LazyStructReader(new YDecoder(decoding.createDecoder(update)), false)
+  let curr = updateDecoder.curr
+  if (curr !== null) {
+    let size = 0
+    let currClient = curr.id.client
+    let stopCounting = curr.id.clock !== 0 // must start at 0
+    let currClock = stopCounting ? 0 : curr.id.clock + curr.length
+    for (; curr !== null; curr = updateDecoder.next()) {
+      if (currClient !== curr.id.client) {
+        if (currClock !== 0) {
+          size++
+          // We found a new client
+          // write what we have to the encoder
+          encoding.writeVarUint(encoder.restEncoder, currClient)
+          encoding.writeVarUint(encoder.restEncoder, currClock)
+        }
+        currClient = curr.id.client
+        currClock = 0
+        stopCounting = curr.id.clock !== 0
+      }
+      // we ignore skips
+      if (curr.constructor === Skip) {
+        stopCounting = true
+      }
+      if (!stopCounting) {
+        currClock = curr.id.clock + curr.length
+      }
+    }
+    // write what we have
+    if (currClock !== 0) {
+      size++
+      encoding.writeVarUint(encoder.restEncoder, currClient)
+      encoding.writeVarUint(encoder.restEncoder, currClock)
+    }
+    // prepend the size of the state vector
+    const enc = encoding.createEncoder()
+    encoding.writeVarUint(enc, size)
+    encoding.writeBinaryEncoder(enc, encoder.restEncoder)
+    encoder.restEncoder = enc
+    return encoder.toUint8Array()
+  } else {
+    encoding.writeVarUint(encoder.restEncoder, 0)
+    return encoder.toUint8Array()
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @return {Uint8Array}
+ */
+export const encodeStateVectorFromUpdate = update => encodeStateVectorFromUpdateV2(update, DSEncoderV1, UpdateDecoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} YDecoder
+ * @return {{ from: Map<number,number>, to: Map<number,number> }}
+ */
+export const parseUpdateMetaV2 = (update, YDecoder = UpdateDecoderV2) => {
+  /**
+   * @type {Map<number, number>}
+   */
+  const from = new Map()
+  /**
+   * @type {Map<number, number>}
+   */
+  const to = new Map()
+  const updateDecoder = new LazyStructReader(new YDecoder(decoding.createDecoder(update)), false)
+  let curr = updateDecoder.curr
+  if (curr !== null) {
+    let currClient = curr.id.client
+    let currClock = curr.id.clock
+    // write the beginning to `from`
+    from.set(currClient, currClock)
+    for (; curr !== null; curr = updateDecoder.next()) {
+      if (currClient !== curr.id.client) {
+        // We found a new client
+        // write the end to `to`
+        to.set(currClient, currClock)
+        // write the beginning to `from`
+        from.set(curr.id.client, curr.id.clock)
+        // update currClient
+        currClient = curr.id.client
+      }
+      currClock = curr.id.clock + curr.length
+    }
+    // write the end to `to`
+    to.set(currClient, currClock)
+  }
+  return { from, to }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @return {{ from: Map<number,number>, to: Map<number,number> }}
+ */
+export const parseUpdateMeta = update => parseUpdateMetaV2(update, UpdateDecoderV1)
+
+/**
+ * This method is intended to slice any kind of struct and retrieve the right part.
+ * It does not handle side-effects, so it should only be used by the lazy-encoder.
+ *
+ * @param {Item | GC | Skip} left
+ * @param {number} diff
+ * @return {Item | GC}
+ */
+const sliceStruct = (left, diff) => {
+  if (left.constructor === GC) {
+    const { client, clock } = left.id
+    return new GC(createID(client, clock + diff), left.length - diff)
+  } else if (left.constructor === Skip) {
+    const { client, clock } = left.id
+    return new Skip(createID(client, clock + diff), left.length - diff)
+  } else {
+    const leftItem = /** @type {Item} */ (left)
+    const { client, clock } = leftItem.id
+    return new Item(
+      createID(client, clock + diff),
+      null,
+      createID(client, clock + diff - 1),
+      null,
+      leftItem.rightOrigin,
+      leftItem.parent,
+      leftItem.parentSub,
+      leftItem.content.splice(diff)
+    )
+  }
+}
+
+/**
+ *
+ * This function works similarly to `readUpdateV2`.
+ *
+ * @param {Array<Uint8Array>} updates
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ * @param {typeof UpdateEncoderV1 | typeof UpdateEncoderV2} [YEncoder]
+ * @return {Uint8Array}
+ */
+export const mergeUpdatesV2 = (updates, YDecoder = UpdateDecoderV2, YEncoder = UpdateEncoderV2) => {
+  if (updates.length === 1) {
+    return updates[0]
+  }
+  const updateDecoders = updates.map(update => new YDecoder(decoding.createDecoder(update)))
+  let lazyStructDecoders = updateDecoders.map(decoder => new LazyStructReader(decoder, true))
+
+  /**
+   * @todo we don't need offset because we always slice before
+   * @type {null | { struct: Item | GC | Skip, offset: number }}
+   */
+  let currWrite = null
+
+  const updateEncoder = new YEncoder()
+  // write structs lazily
+  const lazyStructEncoder = new LazyStructWriter(updateEncoder)
+
+  // Note: We need to ensure that all lazyStructDecoders are fully consumed
+  // Note: Should merge document updates whenever possible - even from different updates
+  // Note: Should handle that some operations cannot be applied yet ()
+
+  while (true) {
+    // Write higher clients first ⇒ sort by clientID & clock and remove decoders without content
+    lazyStructDecoders = lazyStructDecoders.filter(dec => dec.curr !== null)
+    lazyStructDecoders.sort(
+      /** @type {function(any,any):number} */ (dec1, dec2) => {
+        if (dec1.curr.id.client === dec2.curr.id.client) {
+          const clockDiff = dec1.curr.id.clock - dec2.curr.id.clock
+          if (clockDiff === 0) {
+            // @todo remove references to skip since the structDecoders must filter Skips.
+            return dec1.curr.constructor === dec2.curr.constructor
+              ? 0
+              : dec1.curr.constructor === Skip ? 1 : -1 // we are filtering skips anyway.
+          } else {
+            return clockDiff
+          }
+        } else {
+          return dec2.curr.id.client - dec1.curr.id.client
+        }
+      }
+    )
+    if (lazyStructDecoders.length === 0) {
+      break
+    }
+    const currDecoder = lazyStructDecoders[0]
+    // write from currDecoder until the next operation is from another client or if filler-struct
+    // then we need to reorder the decoders and find the next operation to write
+    const firstClient = /** @type {Item | GC} */ (currDecoder.curr).id.client
+
+    if (currWrite !== null) {
+      let curr = /** @type {Item | GC | null} */ (currDecoder.curr)
+      let iterated = false
+
+      // iterate until we find something that we haven't written already
+      // remember: first the high client-ids are written
+      while (curr !== null && curr.id.clock + curr.length <= currWrite.struct.id.clock + currWrite.struct.length && curr.id.client >= currWrite.struct.id.client) {
+        curr = currDecoder.next()
+        iterated = true
+      }
+      if (
+        curr === null || // current decoder is empty
+        curr.id.client !== firstClient || // check whether there is another decoder that has has updates from `firstClient`
+        (iterated && curr.id.clock > currWrite.struct.id.clock + currWrite.struct.length) // the above while loop was used and we are potentially missing updates
+      ) {
+        continue
+      }
+
+      if (firstClient !== currWrite.struct.id.client) {
+        writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+        currWrite = { struct: curr, offset: 0 }
+        currDecoder.next()
+      } else {
+        if (currWrite.struct.id.clock + currWrite.struct.length < curr.id.clock) {
+          // @todo write currStruct & set currStruct = Skip(clock = currStruct.id.clock + currStruct.length, length = curr.id.clock - self.clock)
+          if (currWrite.struct.constructor === Skip) {
+            // extend existing skip
+            currWrite.struct.length = curr.id.clock + curr.length - currWrite.struct.id.clock
+          } else {
+            writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+            const diff = curr.id.clock - currWrite.struct.id.clock - currWrite.struct.length
+            /**
+             * @type {Skip}
+             */
+            const struct = new Skip(createID(firstClient, currWrite.struct.id.clock + currWrite.struct.length), diff)
+            currWrite = { struct, offset: 0 }
+          }
+        } else { // if (currWrite.struct.id.clock + currWrite.struct.length >= curr.id.clock) {
+          const diff = currWrite.struct.id.clock + currWrite.struct.length - curr.id.clock
+          if (diff > 0) {
+            if (currWrite.struct.constructor === Skip) {
+              // prefer to slice Skip because the other struct might contain more information
+              currWrite.struct.length -= diff
+            } else {
+              curr = sliceStruct(curr, diff)
+            }
+          }
+          if (!currWrite.struct.mergeWith(/** @type {any} */ (curr))) {
+            writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+            currWrite = { struct: curr, offset: 0 }
+            currDecoder.next()
+          }
+        }
+      }
+    } else {
+      currWrite = { struct: /** @type {Item | GC} */ (currDecoder.curr), offset: 0 }
+      currDecoder.next()
+    }
+    for (
+      let next = currDecoder.curr;
+      next !== null && next.id.client === firstClient && next.id.clock === currWrite.struct.id.clock + currWrite.struct.length && next.constructor !== Skip;
+      next = currDecoder.next()
+    ) {
+      writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+      currWrite = { struct: next, offset: 0 }
+    }
+  }
+  if (currWrite !== null) {
+    writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+    currWrite = null
+  }
+  finishLazyStructWriting(lazyStructEncoder)
+
+  const dss = updateDecoders.map(decoder => readDeleteSet(decoder))
+  const ds = mergeDeleteSets(dss)
+  writeDeleteSet(updateEncoder, ds)
+  return updateEncoder.toUint8Array()
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {Uint8Array} sv
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ * @param {typeof UpdateEncoderV1 | typeof UpdateEncoderV2} [YEncoder]
+ */
+export const diffUpdateV2 = (update, sv, YDecoder = UpdateDecoderV2, YEncoder = UpdateEncoderV2) => {
+  const state = decodeStateVector(sv)
+  const encoder = new YEncoder()
+  const lazyStructWriter = new LazyStructWriter(encoder)
+  const decoder = new YDecoder(decoding.createDecoder(update))
+  const reader = new LazyStructReader(decoder, false)
+  while (reader.curr) {
+    const curr = reader.curr
+    const currClient = curr.id.client
+    const svClock = state.get(currClient) || 0
+    if (reader.curr.constructor === Skip) {
+      // the first written struct shouldn't be a skip
+      reader.next()
+      continue
+    }
+    if (curr.id.clock + curr.length > svClock) {
+      writeStructToLazyStructWriter(lazyStructWriter, curr, math.max(svClock - curr.id.clock, 0))
+      reader.next()
+      while (reader.curr && reader.curr.id.client === currClient) {
+        writeStructToLazyStructWriter(lazyStructWriter, reader.curr, 0)
+        reader.next()
+      }
+    } else {
+      // read until something new comes up
+      while (reader.curr && reader.curr.id.client === currClient && reader.curr.id.clock + reader.curr.length <= svClock) {
+        reader.next()
+      }
+    }
+  }
+  finishLazyStructWriting(lazyStructWriter)
+  // write ds
+  const ds = readDeleteSet(decoder)
+  writeDeleteSet(encoder, ds)
+  return encoder.toUint8Array()
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {Uint8Array} sv
+ */
+export const diffUpdate = (update, sv) => diffUpdateV2(update, sv, UpdateDecoderV1, UpdateEncoderV1)
+
+/**
+ * @param {LazyStructWriter} lazyWriter
+ */
+const flushLazyStructWriter = lazyWriter => {
+  if (lazyWriter.written > 0) {
+    lazyWriter.clientStructs.push({ written: lazyWriter.written, restEncoder: encoding.toUint8Array(lazyWriter.encoder.restEncoder) })
+    lazyWriter.encoder.restEncoder = encoding.createEncoder()
+    lazyWriter.written = 0
+  }
+}
+
+/**
+ * @param {LazyStructWriter} lazyWriter
+ * @param {Item | GC} struct
+ * @param {number} offset
+ */
+const writeStructToLazyStructWriter = (lazyWriter, struct, offset) => {
+  // flush curr if we start another client
+  if (lazyWriter.written > 0 && lazyWriter.currClient !== struct.id.client) {
+    flushLazyStructWriter(lazyWriter)
+  }
+  if (lazyWriter.written === 0) {
+    lazyWriter.currClient = struct.id.client
+    // write next client
+    lazyWriter.encoder.writeClient(struct.id.client)
+    // write startClock
+    encoding.writeVarUint(lazyWriter.encoder.restEncoder, struct.id.clock + offset)
+  }
+  struct.write(lazyWriter.encoder, offset)
+  lazyWriter.written++
+}
+/**
+ * Call this function when we collected all parts and want to
+ * put all the parts together. After calling this method,
+ * you can continue using the UpdateEncoder.
+ *
+ * @param {LazyStructWriter} lazyWriter
+ */
+const finishLazyStructWriting = (lazyWriter) => {
+  flushLazyStructWriter(lazyWriter)
+
+  // this is a fresh encoder because we called flushCurr
+  const restEncoder = lazyWriter.encoder.restEncoder
+
+  /**
+   * Now we put all the fragments together.
+   * This works similarly to `writeClientsStructs`
+   */
+
+  // write # states that were updated - i.e. the clients
+  encoding.writeVarUint(restEncoder, lazyWriter.clientStructs.length)
+
+  for (let i = 0; i < lazyWriter.clientStructs.length; i++) {
+    const partStructs = lazyWriter.clientStructs[i]
+    /**
+     * Works similarly to `writeStructs`
+     */
+    // write # encoded structs
+    encoding.writeVarUint(restEncoder, partStructs.written)
+    // write the rest of the fragment
+    encoding.writeUint8Array(restEncoder, partStructs.restEncoder)
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} YDecoder
+ * @param {typeof UpdateEncoderV2 | typeof UpdateEncoderV1 } YEncoder
+ */
+export const convertUpdateFormat = (update, YDecoder, YEncoder) => {
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  const updateEncoder = new YEncoder()
+  const lazyWriter = new LazyStructWriter(updateEncoder)
+
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    writeStructToLazyStructWriter(lazyWriter, curr, 0)
+  }
+  finishLazyStructWriting(lazyWriter)
+  const ds = readDeleteSet(updateDecoder)
+  writeDeleteSet(updateEncoder, ds)
+  return updateEncoder.toUint8Array()
+}
+
+/**
+ * @param {Uint8Array} update
+ */
+export const convertUpdateFormatV1ToV2 = update => convertUpdateFormat(update, UpdateDecoderV1, UpdateEncoderV2)
+
+/**
+ * @param {Uint8Array} update
+ */
+export const convertUpdateFormatV2ToV1 = update => convertUpdateFormat(update, UpdateDecoderV2, UpdateEncoderV1)
--- a/src/y.js
+++ b/src/y.js
@@ -1,53 +0,0 @@
-/* @flow */
-'use strict'
-
-function Y (opts) {
-  return new Promise(function (resolve) {
-    var yconfig = new YConfig(opts, function () {
-      yconfig.db.whenUserIdSet(function () {
-        resolve(yconfig)
-      })
-    })
-  })
-}
-
-class YConfig {
-  constructor (opts, callback) {
-    this.db = new Y[opts.db.name](this, opts.db)
-    this.connector = new Y[opts.connector.name](this, opts.connector)
-    this.db.requestTransaction(function * requestTransaction () {
-      // create initial Map type
-      var model = {
-        id: ['_', 0],
-        struct: 'Map',
-        type: 'Map',
-        map: {}
-      }
-      yield* this.store.tryExecute.call(this, model)
-      var root = yield* this.getType(model.id)
-      this.store.y.root = root
-      callback()
-    })
-  }
-  isConnected () {
-    return this.connector.isSynced
-  }
-  disconnect () {
-    return this.connector.disconnect()
-  }
-  reconnect () {
-    return this.connector.reconnect()
-  }
-  destroy () {
-    this.disconnect()
-    this.db.destroy()
-    this.connector = null
-    this.db = null
-  }
-}
-
-if (typeof YConcurrency_TestingMode !== 'undefined') {
-  g.Y = Y //eslint-disable-line
-  // debugger //eslint-disable-line
-}
-Y.utils = {}
--- a/test.html
+++ b/test.html
@@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Testing Yjs</title>
+</head>
+<body>
+  <script type="module" src="./dist/tests.js"></script>
+</body>
+</html>
--- a/tests/compatibility.tests.js
+++ b/tests/compatibility.tests.js
--- a/tests/doc.tests.js
+++ b/tests/doc.tests.js
@@ -0,0 +1,126 @@
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+
+/**
+ * Client id should be changed when an instance receives updates from another client using the same client id.
+ *
+ * @param {t.TestCase} tc
+ */
+export const testClientIdDuplicateChange = tc => {
+  const doc1 = new Y.Doc()
+  doc1.clientID = 0
+  const doc2 = new Y.Doc()
+  doc2.clientID = 0
+  t.assert(doc2.clientID === doc1.clientID)
+  doc1.getArray('a').insert(0, [1, 2])
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc1))
+  t.assert(doc2.clientID !== doc1.clientID)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetTypeEmptyId = tc => {
+  const doc1 = new Y.Doc()
+  doc1.getText('').insert(0, 'h')
+  doc1.getText().insert(1, 'i')
+  const doc2 = new Y.Doc()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc1))
+  t.assert(doc2.getText().toString() === 'hi')
+  t.assert(doc2.getText('').toString() === 'hi')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testToJSON = tc => {
+  const doc = new Y.Doc()
+  t.compare(doc.toJSON(), {}, 'doc.toJSON yields empty object')
+
+  const arr = doc.getArray('array')
+  arr.push(['test1'])
+
+  const map = doc.getMap('map')
+  map.set('k1', 'v1')
+  const map2 = new Y.Map()
+  map.set('k2', map2)
+  map2.set('m2k1', 'm2v1')
+
+  t.compare(doc.toJSON(), {
+    array: ['test1'],
+    map: {
+      k1: 'v1',
+      k2: {
+        m2k1: 'm2v1'
+      }
+    }
+  }, 'doc.toJSON has array and recursive map')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSubdoc = tc => {
+  const doc = new Y.Doc()
+  doc.load() // doesn't do anything
+  {
+    /**
+     * @type {Array<any>|null}
+     */
+    let event = /** @type {any} */ (null)
+    doc.on('subdocs', subdocs => {
+      event = [Array.from(subdocs.added).map(x => x.guid), Array.from(subdocs.removed).map(x => x.guid), Array.from(subdocs.loaded).map(x => x.guid)]
+    })
+    const subdocs = doc.getMap('mysubdocs')
+    const docA = new Y.Doc({ guid: 'a' })
+    docA.load()
+    subdocs.set('a', docA)
+    t.compare(event, [['a'], [], ['a']])
+
+    event = null
+    subdocs.get('a').load()
+    t.assert(event === null)
+
+    event = null
+    subdocs.get('a').destroy()
+    t.compare(event, [['a'], ['a'], []])
+    subdocs.get('a').load()
+    t.compare(event, [[], [], ['a']])
+
+    subdocs.set('b', new Y.Doc({ guid: 'a' }))
+    t.compare(event, [['a'], [], []])
+    subdocs.get('b').load()
+    t.compare(event, [[], [], ['a']])
+
+    const docC = new Y.Doc({ guid: 'c' })
+    docC.load()
+    subdocs.set('c', docC)
+    t.compare(event, [['c'], [], ['c']])
+
+    t.compare(Array.from(doc.getSubdocGuids()), ['a', 'c'])
+  }
+
+  const doc2 = new Y.Doc()
+  {
+    t.compare(Array.from(doc2.getSubdocs()), [])
+    /**
+     * @type {Array<any>|null}
+     */
+    let event = /** @type {any} */ (null)
+    doc2.on('subdocs', subdocs => {
+      event = [Array.from(subdocs.added).map(d => d.guid), Array.from(subdocs.removed).map(d => d.guid), Array.from(subdocs.loaded).map(d => d.guid)]
+    })
+    Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+    t.compare(event, [['a', 'a', 'c'], [], []])
+
+    doc2.getMap('mysubdocs').get('a').load()
+    t.compare(event, [[], [], ['a']])
+
+    t.compare(Array.from(doc2.getSubdocGuids()), ['a', 'c'])
+
+    doc2.getMap('mysubdocs').delete('a')
+    t.compare(event, [[], ['a'], []])
+    t.compare(Array.from(doc2.getSubdocGuids()), ['a', 'c'])
+  }
+}
--- a/tests/encoding.tests.js
+++ b/tests/encoding.tests.js
@@ -0,0 +1,108 @@
+import * as t from 'lib0/testing'
+import * as promise from 'lib0/promise'
+
+import {
+  contentRefs,
+  readContentBinary,
+  readContentDeleted,
+  readContentString,
+  readContentJSON,
+  readContentEmbed,
+  readContentType,
+  readContentFormat,
+  readContentAny,
+  readContentDoc,
+  Doc,
+  PermanentUserData,
+  encodeStateAsUpdate,
+  applyUpdate
+} from '../src/internals.js'
+
+import * as Y from '../src/index.js'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testStructReferences = tc => {
+  t.assert(contentRefs.length === 11)
+  t.assert(contentRefs[1] === readContentDeleted)
+  t.assert(contentRefs[2] === readContentJSON) // TODO: deprecate content json?
+  t.assert(contentRefs[3] === readContentBinary)
+  t.assert(contentRefs[4] === readContentString)
+  t.assert(contentRefs[5] === readContentEmbed)
+  t.assert(contentRefs[6] === readContentFormat)
+  t.assert(contentRefs[7] === readContentType)
+  t.assert(contentRefs[8] === readContentAny)
+  t.assert(contentRefs[9] === readContentDoc)
+  // contentRefs[10] is reserved for Skip structs
+}
+
+/**
+ * There is some custom encoding/decoding happening in PermanentUserData.
+ * This is why it landed here.
+ *
+ * @param {t.TestCase} tc
+ */
+export const testPermanentUserData = async tc => {
+  const ydoc1 = new Doc()
+  const ydoc2 = new Doc()
+  const pd1 = new PermanentUserData(ydoc1)
+  const pd2 = new PermanentUserData(ydoc2)
+  pd1.setUserMapping(ydoc1, ydoc1.clientID, 'user a')
+  pd2.setUserMapping(ydoc2, ydoc2.clientID, 'user b')
+  ydoc1.getText().insert(0, 'xhi')
+  ydoc1.getText().delete(0, 1)
+  ydoc2.getText().insert(0, 'hxxi')
+  ydoc2.getText().delete(1, 2)
+  await promise.wait(10)
+  applyUpdate(ydoc2, encodeStateAsUpdate(ydoc1))
+  applyUpdate(ydoc1, encodeStateAsUpdate(ydoc2))
+
+  // now sync a third doc with same name as doc1 and then create PermanentUserData
+  const ydoc3 = new Doc()
+  applyUpdate(ydoc3, encodeStateAsUpdate(ydoc1))
+  const pd3 = new PermanentUserData(ydoc3)
+  pd3.setUserMapping(ydoc3, ydoc3.clientID, 'user a')
+}
+
+/**
+ * Reported here: https://github.com/yjs/yjs/issues/308
+ * @param {t.TestCase} tc
+ */
+export const testDiffStateVectorOfUpdateIsEmpty = tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {null | Uint8Array}
+   */
+  let sv = /* any */ (null)
+  ydoc.getText().insert(0, 'a')
+  ydoc.on('update', update => {
+    sv = Y.encodeStateVectorFromUpdate(update)
+  })
+  // should produce an update with an empty state vector (because previous ops are missing)
+  ydoc.getText().insert(0, 'a')
+  t.assert(sv !== null && sv.byteLength === 1 && sv[0] === 0)
+}
+
+/**
+ * Reported here: https://github.com/yjs/yjs/issues/308
+ * @param {t.TestCase} tc
+ */
+export const testDiffStateVectorOfUpdateIgnoresSkips = tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const updates = []
+  ydoc.on('update', update => {
+    updates.push(update)
+  })
+  ydoc.getText().insert(0, 'a')
+  ydoc.getText().insert(0, 'b')
+  ydoc.getText().insert(0, 'c')
+  const update13 = Y.mergeUpdates([updates[0], updates[2]])
+  const sv = Y.encodeStateVectorFromUpdate(update13)
+  const state = Y.decodeStateVector(sv)
+  t.assert(state.get(ydoc.clientID) === 1)
+  t.assert(state.size === 1)
+}
--- a/tests/index.js
+++ b/tests/index.js
@@ -0,0 +1,28 @@
+
+import * as map from './y-map.tests.js'
+import * as array from './y-array.tests.js'
+import * as text from './y-text.tests.js'
+import * as xml from './y-xml.tests.js'
+import * as encoding from './encoding.tests.js'
+import * as undoredo from './undo-redo.tests.js'
+import * as compatibility from './compatibility.tests.js'
+import * as doc from './doc.tests.js'
+import * as snapshot from './snapshot.tests.js'
+import * as updates from './updates.tests.js'
+import * as relativePositions from './relativePositions.tests.js'
+
+import { runTests } from 'lib0/testing'
+import { isBrowser, isNode } from 'lib0/environment'
+import * as log from 'lib0/logging'
+
+if (isBrowser) {
+  log.createVConsole(document.body)
+}
+runTests({
+  doc, map, array, text, xml, encoding, undoredo, compatibility, snapshot, updates, relativePositions
+}).then(success => {
+  /* istanbul ignore next */
+  if (isNode) {
+    process.exit(success ? 0 : 1)
+  }
+})
--- a/tests/relativePositions.tests.js
+++ b/tests/relativePositions.tests.js
@@ -0,0 +1,104 @@
+
+import * as Y from '../src/internals'
+import * as t from 'lib0/testing'
+
+/**
+ * @param {Y.YText} ytext
+ */
+const checkRelativePositions = ytext => {
+  // test if all positions are encoded and restored correctly
+  for (let i = 0; i < ytext.length; i++) {
+    // for all types of associations..
+    for (let assoc = -1; assoc < 2; assoc++) {
+      const rpos = Y.createRelativePositionFromTypeIndex(ytext, i, assoc)
+      const encodedRpos = Y.encodeRelativePosition(rpos)
+      const decodedRpos = Y.decodeRelativePosition(encodedRpos)
+      const absPos = /** @type {Y.AbsolutePosition} */ (Y.createAbsolutePositionFromRelativePosition(decodedRpos, /** @type {Y.Doc} */ (ytext.doc)))
+      t.assert(absPos.index === i)
+      t.assert(absPos.assoc === assoc)
+    }
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase1 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '1')
+  ytext.insert(0, 'abc')
+  ytext.insert(0, 'z')
+  ytext.insert(0, 'y')
+  ytext.insert(0, 'x')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase2 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, 'abc')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase3 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, 'abc')
+  ytext.insert(0, '1')
+  ytext.insert(0, 'xyz')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase4 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '1')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase5 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '2')
+  ytext.insert(0, '1')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase6 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionAssociationDifference = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '2')
+  ytext.insert(0, '1')
+  const rposRight = Y.createRelativePositionFromTypeIndex(ytext, 1, 0)
+  const rposLeft = Y.createRelativePositionFromTypeIndex(ytext, 1, -1)
+  ytext.insert(1, 'x')
+  const posRight = Y.createAbsolutePositionFromRelativePosition(rposRight, ydoc)
+  const posLeft = Y.createAbsolutePositionFromRelativePosition(rposLeft, ydoc)
+  t.assert(posRight != null && posRight.index === 2)
+  t.assert(posLeft != null && posLeft.index === 1)
+}
--- a/tests/snapshot.tests.js
+++ b/tests/snapshot.tests.js
@@ -0,0 +1,171 @@
+import { createDocFromSnapshot, Doc, snapshot, YMap } from '../src/internals'
+import * as t from 'lib0/testing'
+import { init } from './testHelper'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicRestoreSnapshot = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, ['hello'])
+  const snap = snapshot(doc)
+  doc.getArray('array').insert(1, ['world'])
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['hello'])
+  t.compare(doc.getArray('array').toArray(), ['hello', 'world'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEmptyRestoreSnapshot = tc => {
+  const doc = new Doc({ gc: false })
+  const snap = snapshot(doc)
+  snap.sv.set(9999, 0)
+  doc.getArray().insert(0, ['world'])
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray().toArray(), [])
+  t.compare(doc.getArray().toArray(), ['world'])
+
+  // now this snapshot reflects the latest state. It shoult still work.
+  const snap2 = snapshot(doc)
+  const docRestored2 = createDocFromSnapshot(doc, snap2)
+  t.compare(docRestored2.getArray().toArray(), ['world'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRestoreSnapshotWithSubType = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, [new YMap()])
+  const subMap = doc.getArray('array').get(0)
+  subMap.set('key1', 'value1')
+
+  const snap = snapshot(doc)
+  subMap.set('key2', 'value2')
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toJSON(), [{
+    key1: 'value1'
+  }])
+  t.compare(doc.getArray('array').toJSON(), [{
+    key1: 'value1',
+    key2: 'value2'
+  }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRestoreDeletedItem1 = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1', 'item2'])
+
+  const snap = snapshot(doc)
+  doc.getArray('array').delete(0)
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item1', 'item2'])
+  t.compare(doc.getArray('array').toArray(), ['item2'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRestoreLeftItem = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1'])
+  doc.getMap('map').set('test', 1)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const snap = snapshot(doc)
+  doc.getArray('array').delete(1)
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item0', 'item1'])
+  t.compare(doc.getArray('array').toArray(), ['item0'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeletedItemsBase = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1'])
+  doc.getArray('array').delete(0)
+  const snap = snapshot(doc)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), [])
+  t.compare(doc.getArray('array').toArray(), ['item0'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeletedItems2 = tc => {
+  const doc = new Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1', 'item2', 'item3'])
+  doc.getArray('array').delete(1)
+  const snap = snapshot(doc)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const docRestored = createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item1', 'item3'])
+  t.compare(doc.getArray('array').toArray(), ['item0', 'item1', 'item3'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDependentChanges = tc => {
+  const { array0, array1, testConnector } = init(tc, { users: 2 })
+
+  if (!array0.doc) {
+    throw new Error('no document 0')
+  }
+  if (!array1.doc) {
+    throw new Error('no document 1')
+  }
+
+  /**
+   * @type Doc
+   */
+  const doc0 = array0.doc
+  /**
+   * @type Doc
+   */
+  const doc1 = array1.doc
+
+  doc0.gc = false
+  doc1.gc = false
+
+  array0.insert(0, ['user1item1'])
+  testConnector.syncAll()
+  array1.insert(1, ['user2item1'])
+  testConnector.syncAll()
+
+  const snap = snapshot(array0.doc)
+
+  array0.insert(2, ['user1item2'])
+  testConnector.syncAll()
+  array1.insert(3, ['user2item2'])
+  testConnector.syncAll()
+
+  const docRestored0 = createDocFromSnapshot(array0.doc, snap)
+  t.compare(docRestored0.getArray('array').toArray(), ['user1item1', 'user2item1'])
+
+  const docRestored1 = createDocFromSnapshot(array1.doc, snap)
+  t.compare(docRestored1.getArray('array').toArray(), ['user1item1', 'user2item1'])
+}
--- a/tests/testHelper.js
+++ b/tests/testHelper.js
@@ -0,0 +1,488 @@
+
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as syncProtocol from 'y-protocols/sync.js'
+import * as object from 'lib0/object'
+import * as Y from '../src/internals.js'
+export * from '../src/internals.js'
+
+if (typeof window !== 'undefined') {
+  // @ts-ignore
+  window.Y = Y // eslint-disable-line
+}
+
+/**
+ * @param {TestYInstance} y // publish message created by `y` to all other online clients
+ * @param {Uint8Array} m
+ */
+const broadcastMessage = (y, m) => {
+  if (y.tc.onlineConns.has(y)) {
+    y.tc.onlineConns.forEach(remoteYInstance => {
+      if (remoteYInstance !== y) {
+        remoteYInstance._receive(m, y)
+      }
+    })
+  }
+}
+
+export let useV2 = false
+
+export const encV1 = {
+  encodeStateAsUpdate: Y.encodeStateAsUpdate,
+  mergeUpdates: Y.mergeUpdates,
+  applyUpdate: Y.applyUpdate,
+  logUpdate: Y.logUpdate,
+  updateEventName: 'update',
+  diffUpdate: Y.diffUpdate
+}
+
+export const encV2 = {
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  mergeUpdates: Y.mergeUpdatesV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  updateEventName: 'updateV2',
+  diffUpdate: Y.diffUpdateV2
+}
+
+export let enc = encV1
+
+const useV1Encoding = () => {
+  useV2 = false
+  enc = encV1
+}
+
+const useV2Encoding = () => {
+  console.error('sync protocol doesnt support v2 protocol yet, fallback to v1 encoding') // @Todo
+  useV2 = false
+  enc = encV1
+}
+
+export class TestYInstance extends Y.Doc {
+  /**
+   * @param {TestConnector} testConnector
+   * @param {number} clientID
+   */
+  constructor (testConnector, clientID) {
+    super()
+    this.userID = clientID // overwriting clientID
+    /**
+     * @type {TestConnector}
+     */
+    this.tc = testConnector
+    /**
+     * @type {Map<TestYInstance, Array<Uint8Array>>}
+     */
+    this.receiving = new Map()
+    testConnector.allConns.add(this)
+    /**
+     * The list of received updates.
+     * We are going to merge them later using Y.mergeUpdates and check if the resulting document is correct.
+     * @type {Array<Uint8Array>}
+     */
+    this.updates = []
+    // set up observe on local model
+    this.on(enc.updateEventName, /** @param {Uint8Array} update @param {any} origin */ (update, origin) => {
+      if (origin !== testConnector) {
+        const encoder = encoding.createEncoder()
+        syncProtocol.writeUpdate(encoder, update)
+        broadcastMessage(this, encoding.toUint8Array(encoder))
+        this.updates.push(update)
+      }
+    })
+    this.connect()
+  }
+
+  /**
+   * Disconnect from TestConnector.
+   */
+  disconnect () {
+    this.receiving = new Map()
+    this.tc.onlineConns.delete(this)
+  }
+
+  /**
+   * Append yourself to the list of known Y instances in testconnector.
+   * Also initiate sync with all clients.
+   */
+  connect () {
+    if (!this.tc.onlineConns.has(this)) {
+      this.tc.onlineConns.add(this)
+      const encoder = encoding.createEncoder()
+      syncProtocol.writeSyncStep1(encoder, this)
+      // publish SyncStep1
+      broadcastMessage(this, encoding.toUint8Array(encoder))
+      this.tc.onlineConns.forEach(remoteYInstance => {
+        if (remoteYInstance !== this) {
+          // remote instance sends instance to this instance
+          const encoder = encoding.createEncoder()
+          syncProtocol.writeSyncStep1(encoder, remoteYInstance)
+          this._receive(encoding.toUint8Array(encoder), remoteYInstance)
+        }
+      })
+    }
+  }
+
+  /**
+   * Receive a message from another client. This message is only appended to the list of receiving messages.
+   * TestConnector decides when this client actually reads this message.
+   *
+   * @param {Uint8Array} message
+   * @param {TestYInstance} remoteClient
+   */
+  _receive (message, remoteClient) {
+    let messages = this.receiving.get(remoteClient)
+    if (messages === undefined) {
+      messages = []
+      this.receiving.set(remoteClient, messages)
+    }
+    messages.push(message)
+  }
+}
+
+/**
+ * Keeps track of TestYInstances.
+ *
+ * The TestYInstances add/remove themselves from the list of connections maiained in this object.
+ * I think it makes sense. Deal with it.
+ */
+export class TestConnector {
+  /**
+   * @param {prng.PRNG} gen
+   */
+  constructor (gen) {
+    /**
+     * @type {Set<TestYInstance>}
+     */
+    this.allConns = new Set()
+    /**
+     * @type {Set<TestYInstance>}
+     */
+    this.onlineConns = new Set()
+    /**
+     * @type {prng.PRNG}
+     */
+    this.prng = gen
+  }
+
+  /**
+   * Create a new Y instance and add it to the list of connections
+   * @param {number} clientID
+   */
+  createY (clientID) {
+    return new TestYInstance(this, clientID)
+  }
+
+  /**
+   * Choose random connection and flush a random message from a random sender.
+   *
+   * If this function was unable to flush a message, because there are no more messages to flush, it returns false. true otherwise.
+   * @return {boolean}
+   */
+  flushRandomMessage () {
+    const gen = this.prng
+    const conns = Array.from(this.onlineConns).filter(conn => conn.receiving.size > 0)
+    if (conns.length > 0) {
+      const receiver = prng.oneOf(gen, conns)
+      const [sender, messages] = prng.oneOf(gen, Array.from(receiver.receiving))
+      const m = messages.shift()
+      if (messages.length === 0) {
+        receiver.receiving.delete(sender)
+      }
+      if (m === undefined) {
+        return this.flushRandomMessage()
+      }
+      const encoder = encoding.createEncoder()
+      // console.log('receive (' + sender.userID + '->' + receiver.userID + '):\n', syncProtocol.stringifySyncMessage(decoding.createDecoder(m), receiver))
+      // do not publish data created when this function is executed (could be ss2 or update message)
+      syncProtocol.readSyncMessage(decoding.createDecoder(m), encoder, receiver, receiver.tc)
+      if (encoding.length(encoder) > 0) {
+        // send reply message
+        sender._receive(encoding.toUint8Array(encoder), receiver)
+      }
+      {
+        // If update message, add the received message to the list of received messages
+        const decoder = decoding.createDecoder(m)
+        const messageType = decoding.readVarUint(decoder)
+        switch (messageType) {
+          case syncProtocol.messageYjsUpdate:
+          case syncProtocol.messageYjsSyncStep2:
+            receiver.updates.push(decoding.readVarUint8Array(decoder))
+            break
+        }
+      }
+      return true
+    }
+    return false
+  }
+
+  /**
+   * @return {boolean} True iff this function actually flushed something
+   */
+  flushAllMessages () {
+    let didSomething = false
+    while (this.flushRandomMessage()) {
+      didSomething = true
+    }
+    return didSomething
+  }
+
+  reconnectAll () {
+    this.allConns.forEach(conn => conn.connect())
+  }
+
+  disconnectAll () {
+    this.allConns.forEach(conn => conn.disconnect())
+  }
+
+  syncAll () {
+    this.reconnectAll()
+    this.flushAllMessages()
+  }
+
+  /**
+   * @return {boolean} Whether it was possible to disconnect a randon connection.
+   */
+  disconnectRandom () {
+    if (this.onlineConns.size === 0) {
+      return false
+    }
+    prng.oneOf(this.prng, Array.from(this.onlineConns)).disconnect()
+    return true
+  }
+
+  /**
+   * @return {boolean} Whether it was possible to reconnect a random connection.
+   */
+  reconnectRandom () {
+    /**
+     * @type {Array<TestYInstance>}
+     */
+    const reconnectable = []
+    this.allConns.forEach(conn => {
+      if (!this.onlineConns.has(conn)) {
+        reconnectable.push(conn)
+      }
+    })
+    if (reconnectable.length === 0) {
+      return false
+    }
+    prng.oneOf(this.prng, reconnectable).connect()
+    return true
+  }
+}
+
+/**
+ * @template T
+ * @param {t.TestCase} tc
+ * @param {{users?:number}} conf
+ * @param {InitTestObjectCallback<T>} [initTestObject]
+ * @return {{testObjects:Array<any>,testConnector:TestConnector,users:Array<TestYInstance>,array0:Y.YArray<any>,array1:Y.YArray<any>,array2:Y.YArray<any>,map0:Y.YMap<any>,map1:Y.YMap<any>,map2:Y.YMap<any>,map3:Y.YMap<any>,text0:Y.YText,text1:Y.YText,text2:Y.YText,xml0:Y.YXmlElement,xml1:Y.YXmlElement,xml2:Y.YXmlElement}}
+ */
+export const init = (tc, { users = 5 } = {}, initTestObject) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const result = {
+    users: []
+  }
+  const gen = tc.prng
+  // choose an encoding approach at random
+  if (prng.bool(gen)) {
+    useV2Encoding()
+  } else {
+    useV1Encoding()
+  }
+
+  const testConnector = new TestConnector(gen)
+  result.testConnector = testConnector
+  for (let i = 0; i < users; i++) {
+    const y = testConnector.createY(i)
+    y.clientID = i
+    result.users.push(y)
+    result['array' + i] = y.getArray('array')
+    result['map' + i] = y.getMap('map')
+    result['xml' + i] = y.get('xml', Y.YXmlElement)
+    result['text' + i] = y.getText('text')
+  }
+  testConnector.syncAll()
+  result.testObjects = result.users.map(initTestObject || (() => null))
+  useV1Encoding()
+  return /** @type {any} */ (result)
+}
+
+/**
+ * 1. reconnect and flush all
+ * 2. user 0 gc
+ * 3. get type content
+ * 4. disconnect & reconnect all (so gc is propagated)
+ * 5. compare os, ds, ss
+ *
+ * @param {Array<TestYInstance>} users
+ */
+export const compare = users => {
+  users.forEach(u => u.connect())
+  while (users[0].tc.flushAllMessages()) {} // eslint-disable-line
+  // For each document, merge all received document updates with Y.mergeUpdates and create a new document which will be added to the list of "users"
+  // This ensures that mergeUpdates works correctly
+  const mergedDocs = users.map(user => {
+    const ydoc = new Y.Doc()
+    enc.applyUpdate(ydoc, enc.mergeUpdates(user.updates))
+    return ydoc
+  })
+  users.push(.../** @type {any} */(mergedDocs))
+  const userArrayValues = users.map(u => u.getArray('array').toJSON())
+  const userMapValues = users.map(u => u.getMap('map').toJSON())
+  const userXmlValues = users.map(u => u.get('xml', Y.YXmlElement).toString())
+  const userTextValues = users.map(u => u.getText('text').toDelta())
+  for (const u of users) {
+    t.assert(u.store.pendingDs === null)
+    t.assert(u.store.pendingStructs === null)
+  }
+  // Test Array iterator
+  t.compare(users[0].getArray('array').toArray(), Array.from(users[0].getArray('array')))
+  // Test Map iterator
+  const ymapkeys = Array.from(users[0].getMap('map').keys())
+  t.assert(ymapkeys.length === Object.keys(userMapValues[0]).length)
+  ymapkeys.forEach(key => t.assert(object.hasProperty(userMapValues[0], key)))
+  /**
+   * @type {Object<string,any>}
+   */
+  const mapRes = {}
+  for (const [k, v] of users[0].getMap('map')) {
+    mapRes[k] = v instanceof Y.AbstractType ? v.toJSON() : v
+  }
+  t.compare(userMapValues[0], mapRes)
+  // Compare all users
+  for (let i = 0; i < users.length - 1; i++) {
+    t.compare(userArrayValues[i].length, users[i].getArray('array').length)
+    t.compare(userArrayValues[i], userArrayValues[i + 1])
+    t.compare(userMapValues[i], userMapValues[i + 1])
+    t.compare(userXmlValues[i], userXmlValues[i + 1])
+    t.compare(userTextValues[i].map(/** @param {any} a */ a => typeof a.insert === 'string' ? a.insert : ' ').join('').length, users[i].getText('text').length)
+    t.compare(userTextValues[i], userTextValues[i + 1], '', (constructor, a, b) => {
+      if (a instanceof Y.AbstractType) {
+        t.compare(a.toJSON(), b.toJSON())
+      } else if (a !== b) {
+        t.fail('Deltas dont match')
+      }
+      return true
+    })
+    t.compare(Y.getStateVector(users[i].store), Y.getStateVector(users[i + 1].store))
+    compareDS(Y.createDeleteSetFromStructStore(users[i].store), Y.createDeleteSetFromStructStore(users[i + 1].store))
+    compareStructStores(users[i].store, users[i + 1].store)
+  }
+  users.map(u => u.destroy())
+}
+
+/**
+ * @param {Y.Item?} a
+ * @param {Y.Item?} b
+ * @return {boolean}
+ */
+export const compareItemIDs = (a, b) => a === b || (a !== null && b != null && Y.compareIDs(a.id, b.id))
+
+/**
+ * @param {Y.StructStore} ss1
+ * @param {Y.StructStore} ss2
+ */
+export const compareStructStores = (ss1, ss2) => {
+  t.assert(ss1.clients.size === ss2.clients.size)
+  for (const [client, structs1] of ss1.clients) {
+    const structs2 = /** @type {Array<Y.AbstractStruct>} */ (ss2.clients.get(client))
+    t.assert(structs2 !== undefined && structs1.length === structs2.length)
+    for (let i = 0; i < structs1.length; i++) {
+      const s1 = structs1[i]
+      const s2 = structs2[i]
+      // checks for abstract struct
+      if (
+        s1.constructor !== s2.constructor ||
+        !Y.compareIDs(s1.id, s2.id) ||
+        s1.deleted !== s2.deleted ||
+        // @ts-ignore
+        s1.length !== s2.length
+      ) {
+        t.fail('Structs dont match')
+      }
+      if (s1 instanceof Y.Item) {
+        if (
+          !(s2 instanceof Y.Item) ||
+          !((s1.left === null && s2.left === null) || (s1.left !== null && s2.left !== null && Y.compareIDs(s1.left.lastId, s2.left.lastId))) ||
+          !compareItemIDs(s1.right, s2.right) ||
+          !Y.compareIDs(s1.origin, s2.origin) ||
+          !Y.compareIDs(s1.rightOrigin, s2.rightOrigin) ||
+          s1.parentSub !== s2.parentSub
+        ) {
+          return t.fail('Items dont match')
+        }
+        // make sure that items are connected correctly
+        t.assert(s1.left === null || s1.left.right === s1)
+        t.assert(s1.right === null || s1.right.left === s1)
+        t.assert(s2.left === null || s2.left.right === s2)
+        t.assert(s2.right === null || s2.right.left === s2)
+      }
+    }
+  }
+}
+
+/**
+ * @param {Y.DeleteSet} ds1
+ * @param {Y.DeleteSet} ds2
+ */
+export const compareDS = (ds1, ds2) => {
+  t.assert(ds1.clients.size === ds2.clients.size)
+  ds1.clients.forEach((deleteItems1, client) => {
+    const deleteItems2 = /** @type {Array<Y.DeleteItem>} */ (ds2.clients.get(client))
+    t.assert(deleteItems2 !== undefined && deleteItems1.length === deleteItems2.length)
+    for (let i = 0; i < deleteItems1.length; i++) {
+      const di1 = deleteItems1[i]
+      const di2 = deleteItems2[i]
+      if (di1.clock !== di2.clock || di1.len !== di2.len) {
+        t.fail('DeleteSets dont match')
+      }
+    }
+  })
+}
+
+/**
+ * @template T
+ * @callback InitTestObjectCallback
+ * @param {TestYInstance} y
+ * @return {T}
+ */
+
+/**
+ * @template T
+ * @param {t.TestCase} tc
+ * @param {Array<function(Y.Doc,prng.PRNG,T):void>} mods
+ * @param {number} iterations
+ * @param {InitTestObjectCallback<T>} [initTestObject]
+ */
+export const applyRandomTests = (tc, mods, iterations, initTestObject) => {
+  const gen = tc.prng
+  const result = init(tc, { users: 5 }, initTestObject)
+  const { testConnector, users } = result
+  for (let i = 0; i < iterations; i++) {
+    if (prng.int32(gen, 0, 100) <= 2) {
+      // 2% chance to disconnect/reconnect a random user
+      if (prng.bool(gen)) {
+        testConnector.disconnectRandom()
+      } else {
+        testConnector.reconnectRandom()
+      }
+    } else if (prng.int32(gen, 0, 100) <= 1) {
+      // 1% chance to flush all
+      testConnector.flushAllMessages()
+    } else if (prng.int32(gen, 0, 100) <= 50) {
+      // 50% chance to flush a random message
+      testConnector.flushRandomMessage()
+    }
+    const user = prng.int32(gen, 0, users.length - 1)
+    const test = prng.oneOf(gen, mods)
+    test(users[user], gen, result.testObjects[user])
+  }
+  compare(users)
+  return result
+}
--- a/tests/undo-redo.tests.js
+++ b/tests/undo-redo.tests.js
@@ -0,0 +1,358 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import {
+  UndoManager
+} from '../src/internals.js'
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoText = tc => {
+  const { testConnector, text0, text1 } = init(tc, { users: 3 })
+  const undoManager = new UndoManager(text0)
+
+  // items that are added & deleted in the same transaction won't be undo
+  text0.insert(0, 'test')
+  text0.delete(0, 4)
+  undoManager.undo()
+  t.assert(text0.toString() === '')
+
+  // follow redone items
+  text0.insert(0, 'a')
+  undoManager.stopCapturing()
+  text0.delete(0, 1)
+  undoManager.stopCapturing()
+  undoManager.undo()
+  t.assert(text0.toString() === 'a')
+  undoManager.undo()
+  t.assert(text0.toString() === '')
+
+  text0.insert(0, 'abc')
+  text1.insert(0, 'xyz')
+  testConnector.syncAll()
+  undoManager.undo()
+  t.assert(text0.toString() === 'xyz')
+  undoManager.redo()
+  t.assert(text0.toString() === 'abcxyz')
+  testConnector.syncAll()
+  text1.delete(0, 1)
+  testConnector.syncAll()
+  undoManager.undo()
+  t.assert(text0.toString() === 'xyz')
+  undoManager.redo()
+  t.assert(text0.toString() === 'bcxyz')
+  // test marks
+  text0.format(1, 3, { bold: true })
+  t.compare(text0.toDelta(), [{ insert: 'b' }, { insert: 'cxy', attributes: { bold: true } }, { insert: 'z' }])
+  undoManager.undo()
+  t.compare(text0.toDelta(), [{ insert: 'bcxyz' }])
+  undoManager.redo()
+  t.compare(text0.toDelta(), [{ insert: 'b' }, { insert: 'cxy', attributes: { bold: true } }, { insert: 'z' }])
+}
+
+/**
+ * Test case to fix #241
+ * @param {t.TestCase} tc
+ */
+export const testDoubleUndo = tc => {
+  const doc = new Y.Doc()
+  const text = doc.getText()
+  text.insert(0, '1221')
+
+  const manager = new Y.UndoManager(text)
+
+  text.insert(2, '3')
+  text.insert(3, '3')
+
+  manager.undo()
+  manager.undo()
+
+  text.insert(2, '3')
+
+  t.compareStrings(text.toString(), '12321')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoMap = tc => {
+  const { testConnector, map0, map1 } = init(tc, { users: 2 })
+  map0.set('a', 0)
+  const undoManager = new UndoManager(map0)
+  map0.set('a', 1)
+  undoManager.undo()
+  t.assert(map0.get('a') === 0)
+  undoManager.redo()
+  t.assert(map0.get('a') === 1)
+  // testing sub-types and if it can restore a whole type
+  const subType = new Y.Map()
+  map0.set('a', subType)
+  subType.set('x', 42)
+  t.compare(map0.toJSON(), /** @type {any} */ ({ a: { x: 42 } }))
+  undoManager.undo()
+  t.assert(map0.get('a') === 1)
+  undoManager.redo()
+  t.compare(map0.toJSON(), /** @type {any} */ ({ a: { x: 42 } }))
+  testConnector.syncAll()
+  // if content is overwritten by another user, undo operations should be skipped
+  map1.set('a', 44)
+  testConnector.syncAll()
+  undoManager.undo()
+  t.assert(map0.get('a') === 44)
+  undoManager.redo()
+  t.assert(map0.get('a') === 44)
+
+  // test setting value multiple times
+  map0.set('b', 'initial')
+  undoManager.stopCapturing()
+  map0.set('b', 'val1')
+  map0.set('b', 'val2')
+  undoManager.stopCapturing()
+  undoManager.undo()
+  t.assert(map0.get('b') === 'initial')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoArray = tc => {
+  const { testConnector, array0, array1 } = init(tc, { users: 3 })
+  const undoManager = new UndoManager(array0)
+  array0.insert(0, [1, 2, 3])
+  array1.insert(0, [4, 5, 6])
+  testConnector.syncAll()
+  t.compare(array0.toArray(), [1, 2, 3, 4, 5, 6])
+  undoManager.undo()
+  t.compare(array0.toArray(), [4, 5, 6])
+  undoManager.redo()
+  t.compare(array0.toArray(), [1, 2, 3, 4, 5, 6])
+  testConnector.syncAll()
+  array1.delete(0, 1) // user1 deletes [1]
+  testConnector.syncAll()
+  undoManager.undo()
+  t.compare(array0.toArray(), [4, 5, 6])
+  undoManager.redo()
+  t.compare(array0.toArray(), [2, 3, 4, 5, 6])
+  array0.delete(0, 5)
+  // test nested structure
+  const ymap = new Y.Map()
+  array0.insert(0, [ymap])
+  t.compare(array0.toJSON(), [{}])
+  undoManager.stopCapturing()
+  ymap.set('a', 1)
+  t.compare(array0.toJSON(), [{ a: 1 }])
+  undoManager.undo()
+  t.compare(array0.toJSON(), [{}])
+  undoManager.undo()
+  t.compare(array0.toJSON(), [2, 3, 4, 5, 6])
+  undoManager.redo()
+  t.compare(array0.toJSON(), [{}])
+  undoManager.redo()
+  t.compare(array0.toJSON(), [{ a: 1 }])
+  testConnector.syncAll()
+  array1.get(0).set('b', 2)
+  testConnector.syncAll()
+  t.compare(array0.toJSON(), [{ a: 1, b: 2 }])
+  undoManager.undo()
+  t.compare(array0.toJSON(), [{ b: 2 }])
+  undoManager.undo()
+  t.compare(array0.toJSON(), [2, 3, 4, 5, 6])
+  undoManager.redo()
+  t.compare(array0.toJSON(), [{ b: 2 }])
+  undoManager.redo()
+  t.compare(array0.toJSON(), [{ a: 1, b: 2 }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoXml = tc => {
+  const { xml0 } = init(tc, { users: 3 })
+  const undoManager = new UndoManager(xml0)
+  const child = new Y.XmlElement('p')
+  xml0.insert(0, [child])
+  const textchild = new Y.XmlText('content')
+  child.insert(0, [textchild])
+  t.assert(xml0.toString() === '<undefined><p>content</p></undefined>')
+  // format textchild and revert that change
+  undoManager.stopCapturing()
+  textchild.format(3, 4, { bold: {} })
+  t.assert(xml0.toString() === '<undefined><p>con<bold>tent</bold></p></undefined>')
+  undoManager.undo()
+  t.assert(xml0.toString() === '<undefined><p>content</p></undefined>')
+  undoManager.redo()
+  t.assert(xml0.toString() === '<undefined><p>con<bold>tent</bold></p></undefined>')
+  xml0.delete(0, 1)
+  t.assert(xml0.toString() === '<undefined></undefined>')
+  undoManager.undo()
+  t.assert(xml0.toString() === '<undefined><p>con<bold>tent</bold></p></undefined>')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoEvents = tc => {
+  const { text0 } = init(tc, { users: 3 })
+  const undoManager = new UndoManager(text0)
+  let counter = 0
+  let receivedMetadata = -1
+  undoManager.on('stack-item-added', /** @param {any} event */ event => {
+    t.assert(event.type != null)
+    t.assert(event.changedParentTypes != null && event.changedParentTypes.has(text0))
+    event.stackItem.meta.set('test', counter++)
+  })
+  undoManager.on('stack-item-popped', /** @param {any} event */ event => {
+    t.assert(event.type != null)
+    t.assert(event.changedParentTypes != null && event.changedParentTypes.has(text0))
+    receivedMetadata = event.stackItem.meta.get('test')
+  })
+  text0.insert(0, 'abc')
+  undoManager.undo()
+  t.assert(receivedMetadata === 0)
+  undoManager.redo()
+  t.assert(receivedMetadata === 1)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTrackClass = tc => {
+  const { users, text0 } = init(tc, { users: 3 })
+  // only track origins that are numbers
+  const undoManager = new UndoManager(text0, { trackedOrigins: new Set([Number]) })
+  users[0].transact(() => {
+    text0.insert(0, 'abc')
+  }, 42)
+  t.assert(text0.toString() === 'abc')
+  undoManager.undo()
+  t.assert(text0.toString() === '')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTypeScope = tc => {
+  const { array0 } = init(tc, { users: 3 })
+  // only track origins that are numbers
+  const text0 = new Y.Text()
+  const text1 = new Y.Text()
+  array0.insert(0, [text0, text1])
+  const undoManager = new UndoManager(text0)
+  const undoManagerBoth = new UndoManager([text0, text1])
+  text1.insert(0, 'abc')
+  t.assert(undoManager.undoStack.length === 0)
+  t.assert(undoManagerBoth.undoStack.length === 1)
+  t.assert(text1.toString() === 'abc')
+  undoManager.undo()
+  t.assert(text1.toString() === 'abc')
+  undoManagerBoth.undo()
+  t.assert(text1.toString() === '')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoDeleteFilter = tc => {
+  /**
+   * @type {Array<Y.Map<any>>}
+   */
+  const array0 = /** @type {any} */ (init(tc, { users: 3 }).array0)
+  const undoManager = new UndoManager(array0, { deleteFilter: item => !(item instanceof Y.Item) || (item.content instanceof Y.ContentType && item.content.type._map.size === 0) })
+  const map0 = new Y.Map()
+  map0.set('hi', 1)
+  const map1 = new Y.Map()
+  array0.insert(0, [map0, map1])
+  undoManager.undo()
+  t.assert(array0.length === 1)
+  array0.get(0)
+  t.assert(Array.from(array0.get(0).keys()).length === 1)
+}
+
+/**
+ * This issue has been reported in https://discuss.yjs.dev/t/undomanager-with-external-updates/454/6
+ * @param {t.TestCase} tc
+ */
+export const testUndoUntilChangePerformed = tc => {
+  const doc = new Y.Doc()
+  const doc2 = new Y.Doc()
+  doc.on('update', update => Y.applyUpdate(doc2, update))
+  doc2.on('update', update => Y.applyUpdate(doc, update))
+
+  const yArray = doc.getArray('array')
+  const yArray2 = doc2.getArray('array')
+  const yMap = new Y.Map()
+  yMap.set('hello', 'world')
+  yArray.push([yMap])
+  const yMap2 = new Y.Map()
+  yMap2.set('key', 'value')
+  yArray.push([yMap2])
+
+  const undoManager = new Y.UndoManager([yArray], { trackedOrigins: new Set([doc.clientID]) })
+  const undoManager2 = new Y.UndoManager([doc2.get('array')], { trackedOrigins: new Set([doc2.clientID]) })
+
+  Y.transact(doc, () => yMap2.set('key', 'value modified'), doc.clientID)
+  undoManager.stopCapturing()
+  Y.transact(doc, () => yMap.set('hello', 'world modified'), doc.clientID)
+  Y.transact(doc2, () => yArray2.delete(0), doc2.clientID)
+  undoManager2.undo()
+  undoManager.undo()
+  t.compareStrings(yMap2.get('key'), 'value')
+}
+
+/**
+ * This issue has been reported in https://github.com/yjs/yjs/issues/317
+ * @param {t.TestCase} tc
+ */
+export const testUndoNestedUndoIssue = tc => {
+  const doc = new Y.Doc({ gc: false })
+  const design = doc.getMap()
+  const undoManager = new Y.UndoManager(design, { captureTimeout: 0 })
+
+  /**
+   * @type {Y.Map<any>}
+   */
+  const text = new Y.Map()
+
+  const blocks1 = new Y.Array()
+  const blocks1block = new Y.Map()
+
+  doc.transact(() => {
+    blocks1block.set('text', 'Type Something')
+    blocks1.push([blocks1block])
+    text.set('blocks', blocks1block)
+    design.set('text', text)
+  })
+
+  const blocks2 = new Y.Array()
+  const blocks2block = new Y.Map()
+  doc.transact(() => {
+    blocks2block.set('text', 'Something')
+    blocks2.push([blocks2block])
+    text.set('blocks', blocks2block)
+  })
+
+  const blocks3 = new Y.Array()
+  const blocks3block = new Y.Map()
+  doc.transact(() => {
+    blocks3block.set('text', 'Something Else')
+    blocks3.push([blocks3block])
+    text.set('blocks', blocks3block)
+  })
+
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Type Something' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Type Something' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
+}
--- a/tests/updates.tests.js
+++ b/tests/updates.tests.js
@@ -0,0 +1,288 @@
+import * as t from 'lib0/testing'
+import { init, compare } from './testHelper.js' // eslint-disable-line
+import * as Y from '../src/index.js'
+import { readClientsStructRefs, readDeleteSet, UpdateDecoderV2, UpdateEncoderV2, writeDeleteSet } from '../src/internals.js'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+
+/**
+ * @typedef {Object} Enc
+ * @property {function(Array<Uint8Array>):Uint8Array} Enc.mergeUpdates
+ * @property {function(Y.Doc):Uint8Array} Enc.encodeStateAsUpdate
+ * @property {function(Y.Doc, Uint8Array):void} Enc.applyUpdate
+ * @property {function(Uint8Array):void} Enc.logUpdate
+ * @property {function(Uint8Array):{from:Map<number,number>,to:Map<number,number>}} Enc.parseUpdateMeta
+ * @property {function(Y.Doc):Uint8Array} Enc.encodeStateVector
+ * @property {function(Uint8Array):Uint8Array} Enc.encodeStateVectorFromUpdate
+ * @property {string} Enc.updateEventName
+ * @property {string} Enc.description
+ * @property {function(Uint8Array, Uint8Array):Uint8Array} Enc.diffUpdate
+ */
+
+/**
+ * @type {Enc}
+ */
+const encV1 = {
+  mergeUpdates: Y.mergeUpdates,
+  encodeStateAsUpdate: Y.encodeStateAsUpdate,
+  applyUpdate: Y.applyUpdate,
+  logUpdate: Y.logUpdate,
+  parseUpdateMeta: Y.parseUpdateMeta,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdate,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'update',
+  description: 'V1',
+  diffUpdate: Y.diffUpdate
+}
+
+/**
+ * @type {Enc}
+ */
+const encV2 = {
+  mergeUpdates: Y.mergeUpdatesV2,
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  parseUpdateMeta: Y.parseUpdateMetaV2,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdateV2,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'updateV2',
+  description: 'V2',
+  diffUpdate: Y.diffUpdateV2
+}
+
+/**
+ * @type {Enc}
+ */
+const encDoc = {
+  mergeUpdates: (updates) => {
+    const ydoc = new Y.Doc({ gc: false })
+    updates.forEach(update => {
+      Y.applyUpdateV2(ydoc, update)
+    })
+    return Y.encodeStateAsUpdateV2(ydoc)
+  },
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  parseUpdateMeta: Y.parseUpdateMetaV2,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdateV2,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'updateV2',
+  description: 'Merge via Y.Doc',
+  /**
+   * @param {Uint8Array} update
+   * @param {Uint8Array} sv
+   */
+  diffUpdate: (update, sv) => {
+    const ydoc = new Y.Doc({ gc: false })
+    Y.applyUpdateV2(ydoc, update)
+    return Y.encodeStateAsUpdateV2(ydoc, sv)
+  }
+}
+
+const encoders = [encV1, encV2, encDoc]
+
+/**
+ * @param {Array<Y.Doc>} users
+ * @param {Enc} enc
+ */
+const fromUpdates = (users, enc) => {
+  const updates = users.map(user =>
+    enc.encodeStateAsUpdate(user)
+  )
+  const ydoc = new Y.Doc()
+  enc.applyUpdate(ydoc, enc.mergeUpdates(updates))
+  return ydoc
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergeUpdates = tc => {
+  const { users, array0, array1 } = init(tc, { users: 3 })
+
+  array0.insert(0, [1])
+  array1.insert(0, [2])
+
+  compare(users)
+  encoders.forEach(enc => {
+    const merged = fromUpdates(users, enc)
+    t.compareArrays(array0.toArray(), merged.getArray('array').toArray())
+  })
+}
+
+/**
+ * @param {Y.Doc} ydoc
+ * @param {Array<Uint8Array>} updates - expecting at least 4 updates
+ * @param {Enc} enc
+ * @param {boolean} hasDeletes
+ */
+const checkUpdateCases = (ydoc, updates, enc, hasDeletes) => {
+  const cases = []
+
+  // Case 1: Simple case, simply merge everything
+  cases.push(enc.mergeUpdates(updates))
+
+  // Case 2: Overlapping updates
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates(updates.slice(2)),
+    enc.mergeUpdates(updates.slice(0, 2))
+  ]))
+
+  // Case 3: Overlapping updates
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates(updates.slice(2)),
+    enc.mergeUpdates(updates.slice(1, 3)),
+    updates[0]
+  ]))
+
+  // Case 4: Separated updates (containing skips)
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates([updates[0], updates[2]]),
+    enc.mergeUpdates([updates[1], updates[3]]),
+    enc.mergeUpdates(updates.slice(4))
+  ]))
+
+  // Case 5: overlapping with many duplicates
+  cases.push(enc.mergeUpdates(cases))
+
+  // const targetState = enc.encodeStateAsUpdate(ydoc)
+  // t.info('Target State: ')
+  // enc.logUpdate(targetState)
+
+  cases.forEach((mergedUpdates, i) => {
+    // t.info('State Case $' + i + ':')
+    // enc.logUpdate(updates)
+    const merged = new Y.Doc({ gc: false })
+    enc.applyUpdate(merged, mergedUpdates)
+    t.compareArrays(merged.getArray().toArray(), ydoc.getArray().toArray())
+    t.compare(enc.encodeStateVector(merged), enc.encodeStateVectorFromUpdate(mergedUpdates))
+
+    if (enc.updateEventName !== 'update') { // @todo should this also work on legacy updates?
+      for (let j = 1; j < updates.length; j++) {
+        const partMerged = enc.mergeUpdates(updates.slice(j))
+        const partMeta = enc.parseUpdateMeta(partMerged)
+        const targetSV = Y.encodeStateVectorFromUpdateV2(Y.mergeUpdatesV2(updates.slice(0, j)))
+        const diffed = enc.diffUpdate(mergedUpdates, targetSV)
+        const diffedMeta = enc.parseUpdateMeta(diffed)
+        t.compare(partMeta, diffedMeta)
+        {
+          // We can'd do the following
+          //  - t.compare(diffed, mergedDeletes)
+          // because diffed contains the set of all deletes.
+          // So we add all deletes from `diffed` to `partDeletes` and compare then
+          const decoder = decoding.createDecoder(diffed)
+          const updateDecoder = new UpdateDecoderV2(decoder)
+          readClientsStructRefs(updateDecoder, new Y.Doc())
+          const ds = readDeleteSet(updateDecoder)
+          const updateEncoder = new UpdateEncoderV2()
+          encoding.writeVarUint(updateEncoder.restEncoder, 0) // 0 structs
+          writeDeleteSet(updateEncoder, ds)
+          const deletesUpdate = updateEncoder.toUint8Array()
+          const mergedDeletes = Y.mergeUpdatesV2([deletesUpdate, partMerged])
+          if (!hasDeletes || enc !== encDoc) {
+            // deletes will almost definitely lead to different encoders because of the mergeStruct feature that is present in encDoc
+            t.compare(diffed, mergedDeletes)
+          }
+        }
+      }
+    }
+
+    const meta = enc.parseUpdateMeta(mergedUpdates)
+    meta.from.forEach((clock, client) => t.assert(clock === 0))
+    meta.to.forEach((clock, client) => {
+      const structs = /** @type {Array<Y.Item>} */ (merged.store.clients.get(client))
+      const lastStruct = structs[structs.length - 1]
+      t.assert(lastStruct.id.clock + lastStruct.length === clock)
+    })
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergeUpdates1 = tc => {
+  encoders.forEach((enc, i) => {
+    t.info(`Using encoder: ${enc.description}`)
+    const ydoc = new Y.Doc({ gc: false })
+    const updates = /** @type {Array<Uint8Array>} */ ([])
+    ydoc.on(enc.updateEventName, update => { updates.push(update) })
+
+    const array = ydoc.getArray()
+    array.insert(0, [1])
+    array.insert(0, [2])
+    array.insert(0, [3])
+    array.insert(0, [4])
+
+    checkUpdateCases(ydoc, updates, enc, false)
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergeUpdates2 = tc => {
+  encoders.forEach((enc, i) => {
+    t.info(`Using encoder: ${enc.description}`)
+    const ydoc = new Y.Doc({ gc: false })
+    const updates = /** @type {Array<Uint8Array>} */ ([])
+    ydoc.on(enc.updateEventName, update => { updates.push(update) })
+
+    const array = ydoc.getArray()
+    array.insert(0, [1, 2])
+    array.delete(1, 1)
+    array.insert(0, [3, 4])
+    array.delete(1, 2)
+
+    checkUpdateCases(ydoc, updates, enc, true)
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergePendingUpdates = tc => {
+  const yDoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const serverUpdates = []
+  yDoc.on('update', (update, origin, c) => {
+    serverUpdates.splice(serverUpdates.length, 0, update)
+  })
+  const yText = yDoc.getText('textBlock')
+  yText.applyDelta([{ insert: 'r' }])
+  yText.applyDelta([{ insert: 'o' }])
+  yText.applyDelta([{ insert: 'n' }])
+  yText.applyDelta([{ insert: 'e' }])
+  yText.applyDelta([{ insert: 'n' }])
+
+  const yDoc1 = new Y.Doc()
+  Y.applyUpdate(yDoc1, serverUpdates[0])
+  const update1 = Y.encodeStateAsUpdate(yDoc1)
+
+  const yDoc2 = new Y.Doc()
+  Y.applyUpdate(yDoc2, update1)
+  Y.applyUpdate(yDoc2, serverUpdates[1])
+  const update2 = Y.encodeStateAsUpdate(yDoc2)
+
+  const yDoc3 = new Y.Doc()
+  Y.applyUpdate(yDoc3, update2)
+  Y.applyUpdate(yDoc3, serverUpdates[3])
+  const update3 = Y.encodeStateAsUpdate(yDoc3)
+
+  const yDoc4 = new Y.Doc()
+  Y.applyUpdate(yDoc4, update3)
+  Y.applyUpdate(yDoc4, serverUpdates[2])
+  const update4 = Y.encodeStateAsUpdate(yDoc4)
+
+  const yDoc5 = new Y.Doc()
+  Y.applyUpdate(yDoc5, update4)
+  Y.applyUpdate(yDoc5, serverUpdates[4])
+  // @ts-ignore
+  const update5 = Y.encodeStateAsUpdate(yDoc5) // eslint-disable-line
+
+  const yText5 = yDoc5.getText('textBlock')
+  t.compareStrings(yText5.toString(), 'nenor')
+}
--- a/tests/y-array.tests.js
+++ b/tests/y-array.tests.js
@@ -0,0 +1,632 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+import * as math from 'lib0/math'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicUpdate = tc => {
+  const doc1 = new Y.Doc()
+  const doc2 = new Y.Doc()
+  doc1.getArray('array').insert(0, ['hi'])
+  const update = Y.encodeStateAsUpdate(doc1)
+  Y.applyUpdate(doc2, update)
+  t.compare(doc2.getArray('array').toArray(), ['hi'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSlice = tc => {
+  const doc1 = new Y.Doc()
+  const arr = doc1.getArray('array')
+  arr.insert(0, [1, 2, 3])
+  t.compareArrays(arr.slice(0), [1, 2, 3])
+  t.compareArrays(arr.slice(1), [2, 3])
+  t.compareArrays(arr.slice(0, -1), [1, 2])
+  arr.insert(0, [0])
+  t.compareArrays(arr.slice(0), [0, 1, 2, 3])
+  t.compareArrays(arr.slice(0, 2), [0, 1])
+}
+
+/**
+ * Debugging yjs#297 - a critical bug connected to the search-marker approach
+ *
+ * @param {t.TestCase} tc
+ */
+export const testLengthIssue = tc => {
+  const doc1 = new Y.Doc()
+  const arr = doc1.getArray('array')
+  arr.push([0, 1, 2, 3])
+  arr.delete(0)
+  arr.insert(0, [0])
+  t.assert(arr.length === arr.toArray().length)
+  doc1.transact(() => {
+    arr.delete(1)
+    t.assert(arr.length === arr.toArray().length)
+    arr.insert(1, [1])
+    t.assert(arr.length === arr.toArray().length)
+    arr.delete(2)
+    t.assert(arr.length === arr.toArray().length)
+    arr.insert(2, [2])
+    t.assert(arr.length === arr.toArray().length)
+  })
+  t.assert(arr.length === arr.toArray().length)
+  arr.delete(1)
+  t.assert(arr.length === arr.toArray().length)
+  arr.insert(1, [1])
+  t.assert(arr.length === arr.toArray().length)
+}
+
+/**
+ * Debugging yjs#314
+ *
+ * @param {t.TestCase} tc
+ */
+export const testLengthIssue2 = tc => {
+  const doc = new Y.Doc()
+  const next = doc.getArray()
+  doc.transact(() => {
+    next.insert(0, ['group2'])
+  })
+  doc.transact(() => {
+    next.insert(1, ['rectangle3'])
+  })
+  doc.transact(() => {
+    next.delete(0)
+    next.insert(0, ['rectangle3'])
+  })
+  next.delete(1)
+  doc.transact(() => {
+    next.insert(1, ['ellipse4'])
+  })
+  doc.transact(() => {
+    next.insert(2, ['ellipse3'])
+  })
+  doc.transact(() => {
+    next.insert(3, ['ellipse2'])
+  })
+  doc.transact(() => {
+    doc.transact(() => {
+      t.fails(() => {
+        next.insert(5, ['rectangle2'])
+      })
+      next.insert(4, ['rectangle2'])
+    })
+    doc.transact(() => {
+      // this should not throw an error message
+      next.delete(4)
+    })
+  })
+  console.log(next.toArray())
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeleteInsert = tc => {
+  const { users, array0 } = init(tc, { users: 2 })
+  array0.delete(0, 0)
+  t.describe('Does not throw when deleting zero elements with position 0')
+  t.fails(() => {
+    array0.delete(1, 1)
+  })
+  array0.insert(0, ['A'])
+  array0.delete(1, 0)
+  t.describe('Does not throw when deleting zero elements with valid position 1')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertThreeElementsTryRegetProperty = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, [1, true, false])
+  t.compare(array0.toJSON(), [1, true, false], '.toJSON() works')
+  testConnector.flushAllMessages()
+  t.compare(array1.toJSON(), [1, true, false], '.toJSON() works after sync')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testConcurrentInsertWithThreeConflicts = tc => {
+  const { users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, [0])
+  array1.insert(0, [1])
+  array2.insert(0, [2])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testConcurrentInsertDeleteWithThreeConflicts = tc => {
+  const { testConnector, users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  array0.insert(1, [0])
+  array1.delete(0)
+  array1.delete(1, 1)
+  array2.insert(1, [2])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertionsInLateSync = tc => {
+  const { testConnector, users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  users[2].disconnect()
+  array0.insert(1, ['user0'])
+  array1.insert(1, ['user1'])
+  array2.insert(1, ['user2'])
+  users[1].connect()
+  users[2].connect()
+  testConnector.flushAllMessages()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDisconnectReallyPreventsSendingMessages = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  users[2].disconnect()
+  array0.insert(1, ['user0'])
+  array1.insert(1, ['user1'])
+  t.compare(array0.toJSON(), ['x', 'user0', 'y'])
+  t.compare(array1.toJSON(), ['x', 'user1', 'y'])
+  users[1].connect()
+  users[2].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeletionsInLateSync = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  array1.delete(1, 1)
+  array0.delete(0, 2)
+  users[1].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertThenMergeDeleteOnSync = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  users[0].disconnect()
+  array1.delete(0, 3)
+  users[0].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEvents = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>?}
+   */
+  let event = null
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, [0, 1, 2])
+  t.assert(event !== null)
+  event = null
+  array0.delete(0)
+  t.assert(event !== null)
+  event = null
+  array0.delete(0, 2)
+  t.assert(event !== null)
+  event = null
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testNestedObserverEvents = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<number>}
+   */
+  const vals = []
+  array0.observe(e => {
+    if (array0.length === 1) {
+      // inserting, will call this observer again
+      // we expect that this observer is called after this event handler finishedn
+      array0.insert(1, [1])
+      vals.push(0)
+    } else {
+      // this should be called the second time an element is inserted (above case)
+      vals.push(1)
+    }
+  })
+  array0.insert(0, [0])
+  t.compareArrays(vals, [0, 1])
+  t.compareArrays(array0.toArray(), [0, 1])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEventsForTypes = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>|null}
+   */
+  let event = null
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, [new Y.Array()])
+  t.assert(event !== null)
+  event = null
+  array0.delete(0)
+  t.assert(event !== null)
+  event = null
+  compare(users)
+}
+
+/**
+ * This issue has been reported in https://discuss.yjs.dev/t/order-in-which-events-yielded-by-observedeep-should-be-applied/261/2
+ *
+ * Deep observers generate multiple events. When an array added at item at, say, position 0,
+ * and item 1 changed then the array-add event should fire first so that the change event
+ * path is correct. A array binding might lead to an inconsistent state otherwise.
+ *
+ * @param {t.TestCase} tc
+ */
+export const testObserveDeepEventOrder = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<any>}
+   */
+  let events = []
+  array0.observeDeep(e => {
+    events = e
+  })
+  array0.insert(0, [new Y.Map()])
+  users[0].transact(() => {
+    array0.get(0).set('a', 'a')
+    array0.insert(0, [0])
+  })
+  for (let i = 1; i < events.length; i++) {
+    t.assert(events[i - 1].path.length <= events[i].path.length, 'path size increases, fire top-level events first')
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testChangeEvent = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let changes = null
+  array0.observe(e => {
+    changes = e.changes
+  })
+  const newArr = new Y.Array()
+  array0.insert(0, [newArr, 4, 'dtrn'])
+  t.assert(changes !== null && changes.added.size === 2 && changes.deleted.size === 0)
+  t.compare(changes.delta, [{ insert: [newArr, 4, 'dtrn'] }])
+  changes = null
+  array0.delete(0, 2)
+  t.assert(changes !== null && changes.added.size === 0 && changes.deleted.size === 2)
+  t.compare(changes.delta, [{ delete: 2 }])
+  changes = null
+  array0.insert(1, [0.1])
+  t.assert(changes !== null && changes.added.size === 1 && changes.deleted.size === 0)
+  t.compare(changes.delta, [{ retain: 1 }, { insert: [0.1] }])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEventsForTypes2 = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<Object<string,any>>}
+   */
+  const events = []
+  array0.observe(e => {
+    events.push(e)
+  })
+  array0.insert(0, ['hi', new Y.Map()])
+  t.assert(events.length === 1, 'Event is triggered exactly once for insertion of two elements')
+  array0.delete(1)
+  t.assert(events.length === 2, 'Event is triggered exactly once for deletion')
+  compare(users)
+}
+
+/**
+ * This issue has been reported here https://github.com/yjs/yjs/issues/155
+ * @param {t.TestCase} tc
+ */
+export const testNewChildDoesNotEmitEventInTransaction = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  let fired = false
+  users[0].transact(() => {
+    const newMap = new Y.Map()
+    newMap.observe(() => {
+      fired = true
+    })
+    array0.insert(0, [newMap])
+    newMap.set('tst', 42)
+  })
+  t.assert(!fired, 'Event does not trigger')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGarbageCollector = tc => {
+  const { testConnector, users, array0 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  users[0].disconnect()
+  array0.delete(0, 3)
+  users[0].connect()
+  testConnector.flushAllMessages()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEventTargetIsSetCorrectlyOnLocal = tc => {
+  const { array0, users } = init(tc, { users: 3 })
+  /**
+   * @type {any}
+   */
+  let event
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, ['stuff'])
+  t.assert(event.target === array0, '"target" property is set correctly')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEventTargetIsSetCorrectlyOnRemote = tc => {
+  const { testConnector, array0, array1, users } = init(tc, { users: 3 })
+  /**
+   * @type {any}
+   */
+  let event
+  array0.observe(e => {
+    event = e
+  })
+  array1.insert(0, ['stuff'])
+  testConnector.flushAllMessages()
+  t.assert(event.target === array0, '"target" property is set correctly')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testIteratingArrayContainingTypes = tc => {
+  const y = new Y.Doc()
+  const arr = y.getArray('arr')
+  const numItems = 10
+  for (let i = 0; i < numItems; i++) {
+    const map = new Y.Map()
+    map.set('value', i)
+    arr.push([map])
+  }
+  let cnt = 0
+  for (const item of arr) {
+    t.assert(item.get('value') === cnt++, 'value is correct')
+  }
+  y.destroy()
+}
+
+let _uniqueNumber = 0
+const getUniqueNumber = () => _uniqueNumber++
+
+/**
+ * @type {Array<function(Doc,prng.PRNG,any):void>}
+ */
+const arrayTransactions = [
+  function insert (user, gen) {
+    const yarray = user.getArray('array')
+    const uniqueNumber = getUniqueNumber()
+    const content = []
+    const len = prng.int32(gen, 1, 4)
+    for (let i = 0; i < len; i++) {
+      content.push(uniqueNumber)
+    }
+    const pos = prng.int32(gen, 0, yarray.length)
+    const oldContent = yarray.toArray()
+    yarray.insert(pos, content)
+    oldContent.splice(pos, 0, ...content)
+    t.compareArrays(yarray.toArray(), oldContent) // we want to make sure that fastSearch markers insert at the correct position
+  },
+  function insertTypeArray (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Array()])
+    const array2 = yarray.get(pos)
+    array2.insert(0, [1, 2, 3, 4])
+  },
+  function insertTypeMap (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Map()])
+    const map = yarray.get(pos)
+    map.set('someprop', 42)
+    map.set('someprop', 43)
+    map.set('someprop', 44)
+  },
+  function insertTypeNull (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [null])
+  },
+  function _delete (user, gen) {
+    const yarray = user.getArray('array')
+    const length = yarray.length
+    if (length > 0) {
+      let somePos = prng.int32(gen, 0, length - 1)
+      let delLength = prng.int32(gen, 1, math.min(2, length - somePos))
+      if (prng.bool(gen)) {
+        const type = yarray.get(somePos)
+        if (type instanceof Y.Array && type.length > 0) {
+          somePos = prng.int32(gen, 0, type.length - 1)
+          delLength = prng.int32(gen, 0, math.min(2, type.length - somePos))
+          type.delete(somePos, delLength)
+        }
+      } else {
+        const oldContent = yarray.toArray()
+        yarray.delete(somePos, delLength)
+        oldContent.splice(somePos, delLength)
+        t.compareArrays(yarray.toArray(), oldContent)
+      }
+    }
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests6 = tc => {
+  applyRandomTests(tc, arrayTransactions, 6)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests40 = tc => {
+  applyRandomTests(tc, arrayTransactions, 40)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests42 = tc => {
+  applyRandomTests(tc, arrayTransactions, 42)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests43 = tc => {
+  applyRandomTests(tc, arrayTransactions, 43)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests44 = tc => {
+  applyRandomTests(tc, arrayTransactions, 44)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests45 = tc => {
+  applyRandomTests(tc, arrayTransactions, 45)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests46 = tc => {
+  applyRandomTests(tc, arrayTransactions, 46)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests300 = tc => {
+  applyRandomTests(tc, arrayTransactions, 300)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests400 = tc => {
+  applyRandomTests(tc, arrayTransactions, 400)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests500 = tc => {
+  applyRandomTests(tc, arrayTransactions, 500)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests600 = tc => {
+  applyRandomTests(tc, arrayTransactions, 600)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests1000 = tc => {
+  applyRandomTests(tc, arrayTransactions, 1000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests1800 = tc => {
+  applyRandomTests(tc, arrayTransactions, 1800)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests3000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 3000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests5000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 5000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests30000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 30000)
+}
--- a/tests/y-map.tests.js
+++ b/tests/y-map.tests.js
@@ -0,0 +1,680 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import {
+  compareIDs
+} from '../src/internals.js'
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMapHavingIterableAsConstructorParamTests = tc => {
+  const { map0 } = init(tc, { users: 1 })
+
+  const m1 = new Y.Map(Object.entries({ number: 1, string: 'hello' }))
+  map0.set('m1', m1)
+  t.assert(m1.get('number') === 1)
+  t.assert(m1.get('string') === 'hello')
+
+  const m2 = new Y.Map([
+    ['object', { x: 1 }],
+    ['boolean', true]
+  ])
+  map0.set('m2', m2)
+  t.assert(m2.get('object').x === 1)
+  t.assert(m2.get('boolean') === true)
+
+  const m3 = new Y.Map([...m1, ...m2])
+  map0.set('m3', m3)
+  t.assert(m3.get('number') === 1)
+  t.assert(m3.get('string') === 'hello')
+  t.assert(m3.get('object').x === 1)
+  t.assert(m3.get('boolean') === true)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicMapTests = tc => {
+  const { testConnector, users, map0, map1, map2 } = init(tc, { users: 3 })
+  users[2].disconnect()
+
+  map0.set('null', null)
+  map0.set('number', 1)
+  map0.set('string', 'hello Y')
+  map0.set('object', { key: { key2: 'value' } })
+  map0.set('y-map', new Y.Map())
+  map0.set('boolean1', true)
+  map0.set('boolean0', false)
+  const map = map0.get('y-map')
+  map.set('y-array', new Y.Array())
+  const array = map.get('y-array')
+  array.insert(0, [0])
+  array.insert(0, [-1])
+
+  t.assert(map0.get('null') === null, 'client 0 computed the change (null)')
+  t.assert(map0.get('number') === 1, 'client 0 computed the change (number)')
+  t.assert(map0.get('string') === 'hello Y', 'client 0 computed the change (string)')
+  t.assert(map0.get('boolean0') === false, 'client 0 computed the change (boolean)')
+  t.assert(map0.get('boolean1') === true, 'client 0 computed the change (boolean)')
+  t.compare(map0.get('object'), { key: { key2: 'value' } }, 'client 0 computed the change (object)')
+  t.assert(map0.get('y-map').get('y-array').get(0) === -1, 'client 0 computed the change (type)')
+  t.assert(map0.size === 7, 'client 0 map has correct size')
+
+  users[2].connect()
+  testConnector.flushAllMessages()
+
+  t.assert(map1.get('null') === null, 'client 1 received the update (null)')
+  t.assert(map1.get('number') === 1, 'client 1 received the update (number)')
+  t.assert(map1.get('string') === 'hello Y', 'client 1 received the update (string)')
+  t.assert(map1.get('boolean0') === false, 'client 1 computed the change (boolean)')
+  t.assert(map1.get('boolean1') === true, 'client 1 computed the change (boolean)')
+  t.compare(map1.get('object'), { key: { key2: 'value' } }, 'client 1 received the update (object)')
+  t.assert(map1.get('y-map').get('y-array').get(0) === -1, 'client 1 received the update (type)')
+  t.assert(map1.size === 7, 'client 1 map has correct size')
+
+  // compare disconnected user
+  t.assert(map2.get('null') === null, 'client 2 received the update (null) - was disconnected')
+  t.assert(map2.get('number') === 1, 'client 2 received the update (number) - was disconnected')
+  t.assert(map2.get('string') === 'hello Y', 'client 2 received the update (string) - was disconnected')
+  t.assert(map2.get('boolean0') === false, 'client 2 computed the change (boolean)')
+  t.assert(map2.get('boolean1') === true, 'client 2 computed the change (boolean)')
+  t.compare(map2.get('object'), { key: { key2: 'value' } }, 'client 2 received the update (object) - was disconnected')
+  t.assert(map2.get('y-map').get('y-array').get(0) === -1, 'client 2 received the update (type) - was disconnected')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapProperty = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 2 })
+  map0.set('stuff', 'stuffy')
+  map0.set('undefined', undefined)
+  map0.set('null', null)
+  t.compare(map0.get('stuff'), 'stuffy')
+
+  testConnector.flushAllMessages()
+
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'stuffy')
+    t.assert(u.get('undefined') === undefined, 'undefined')
+    t.compare(u.get('null'), null, 'null')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapSetsYmap = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  const map = map0.set('Map', new Y.Map())
+  t.assert(map0.get('Map') === map)
+  map.set('one', 1)
+  t.compare(map.get('one'), 1)
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapSetsYarray = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  const array = map0.set('Array', new Y.Array())
+  t.assert(array === map0.get('Array'))
+  array.insert(0, [1, 2, 3])
+  // @ts-ignore
+  t.compare(map0.toJSON(), { Array: [1, 2, 3] })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertySyncs = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 2 })
+  map0.set('stuff', 'stuffy')
+  t.compare(map0.get('stuff'), 'stuffy')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'stuffy')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertyWithConflict = tc => {
+  const { testConnector, users, map0, map1 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'c1')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSizeAndDeleteOfMapProperty = tc => {
+  const { map0 } = init(tc, { users: 1 })
+  map0.set('stuff', 'c0')
+  map0.set('otherstuff', 'c1')
+  t.assert(map0.size === 2, `map size is ${map0.size} expected 2`)
+  map0.delete('stuff')
+  t.assert(map0.size === 1, `map size after delete is ${map0.size}, expected 1`)
+  map0.delete('otherstuff')
+  t.assert(map0.size === 0, `map size after delete is ${map0.size}, expected 0`)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetAndDeleteOfMapProperty = tc => {
+  const { testConnector, users, map0, map1 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.delete('stuff')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetAndClearOfMapProperties = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 1 })
+  map0.set('stuff', 'c0')
+  map0.set('otherstuff', 'c1')
+  map0.clear()
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+    t.assert(u.get('otherstuff') === undefined)
+    t.assert(u.size === 0, `map size after clear is ${u.size}, expected 0`)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetAndClearOfMapPropertiesWithConflicts = tc => {
+  const { testConnector, users, map0, map1, map2, map3 } = init(tc, { users: 4 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  map0.set('otherstuff', 'c0')
+  map1.set('otherstuff', 'c1')
+  map2.set('otherstuff', 'c2')
+  map3.set('otherstuff', 'c3')
+  map3.clear()
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+    t.assert(u.get('otherstuff') === undefined)
+    t.assert(u.size === 0, `map size after clear is ${u.size}, expected 0`)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertyWithThreeConflicts = tc => {
+  const { testConnector, users, map0, map1, map2 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'c3')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetAndDeleteOfMapPropertyWithThreeConflicts = tc => {
+  const { testConnector, users, map0, map1, map2, map3 } = init(tc, { users: 4 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  map0.set('stuff', 'deleteme')
+  map1.set('stuff', 'c1')
+  map2.set('stuff', 'c2')
+  map3.set('stuff', 'c3')
+  map3.delete('stuff')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testObserveDeepProperties = tc => {
+  const { testConnector, users, map1, map2, map3 } = init(tc, { users: 4 })
+  const _map1 = map1.set('map', new Y.Map())
+  let calls = 0
+  let dmapid
+  map1.observeDeep(events => {
+    events.forEach(event => {
+      calls++
+      // @ts-ignore
+      t.assert(event.keysChanged.has('deepmap'))
+      t.assert(event.path.length === 1)
+      t.assert(event.path[0] === 'map')
+      // @ts-ignore
+      dmapid = event.target.get('deepmap')._item.id
+    })
+  })
+  testConnector.flushAllMessages()
+  const _map3 = map3.get('map')
+  _map3.set('deepmap', new Y.Map())
+  testConnector.flushAllMessages()
+  const _map2 = map2.get('map')
+  _map2.set('deepmap', new Y.Map())
+  testConnector.flushAllMessages()
+  const dmap1 = _map1.get('deepmap')
+  const dmap2 = _map2.get('deepmap')
+  const dmap3 = _map3.get('deepmap')
+  t.assert(calls > 0)
+  t.assert(compareIDs(dmap1._item.id, dmap2._item.id))
+  t.assert(compareIDs(dmap1._item.id, dmap3._item.id))
+  // @ts-ignore we want the possibility of dmapid being undefined
+  t.assert(compareIDs(dmap1._item.id, dmapid))
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testObserversUsingObservedeep = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Array<Array<string|number>>}
+   */
+  const pathes = []
+  let calls = 0
+  map0.observeDeep(events => {
+    events.forEach(event => {
+      pathes.push(event.path)
+    })
+    calls++
+  })
+  map0.set('map', new Y.Map())
+  map0.get('map').set('array', new Y.Array())
+  map0.get('map').get('array').insert(0, ['content'])
+  t.assert(calls === 3)
+  t.compare(pathes, [[], ['map'], ['map', 'array']])
+  compare(users)
+}
+
+// TODO: Test events in Y.Map
+/**
+ * @param {Object<string,any>} is
+ * @param {Object<string,any>} should
+ */
+const compareEvent = (is, should) => {
+  for (const key in should) {
+    t.compare(should[key], is[key])
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testThrowsAddAndUpdateAndDeleteEvents = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e // just put it on event, should be thrown synchronously anyway
+  })
+  map0.set('stuff', 4)
+  compareEvent(event, {
+    target: map0,
+    keysChanged: new Set(['stuff'])
+  })
+  // update, oldValue is in contents
+  map0.set('stuff', new Y.Array())
+  compareEvent(event, {
+    target: map0,
+    keysChanged: new Set(['stuff'])
+  })
+  // update, oldValue is in opContents
+  map0.set('stuff', 5)
+  // delete
+  map0.delete('stuff')
+  compareEvent(event, {
+    keysChanged: new Set(['stuff']),
+    target: map0
+  })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testThrowsDeleteEventsOnClear = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e // just put it on event, should be thrown synchronously anyway
+  })
+  // set values
+  map0.set('stuff', 4)
+  map0.set('otherstuff', new Y.Array())
+  // clear
+  map0.clear()
+  compareEvent(event, {
+    keysChanged: new Set(['stuff', 'otherstuff']),
+    target: map0
+  })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testChangeEvent = tc => {
+  const { map0, users } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let changes = null
+  /**
+   * @type {any}
+   */
+  let keyChange = null
+  map0.observe(e => {
+    changes = e.changes
+  })
+  map0.set('a', 1)
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  map0.set('a', 2)
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'update' && keyChange.oldValue === 1)
+  users[0].transact(() => {
+    map0.set('a', 3)
+    map0.set('a', 4)
+  })
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'update' && keyChange.oldValue === 2)
+  users[0].transact(() => {
+    map0.set('b', 1)
+    map0.set('b', 2)
+  })
+  keyChange = changes.keys.get('b')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  users[0].transact(() => {
+    map0.set('c', 1)
+    map0.delete('c')
+  })
+  t.assert(changes !== null && changes.keys.size === 0)
+  users[0].transact(() => {
+    map0.set('d', 1)
+    map0.set('d', 2)
+  })
+  keyChange = changes.keys.get('d')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapEventExceptionsShouldCompleteTransaction = tc => {
+  const doc = new Y.Doc()
+  const map = doc.getMap('map')
+
+  let updateCalled = false
+  let throwingObserverCalled = false
+  let throwingDeepObserverCalled = false
+  doc.on('update', () => {
+    updateCalled = true
+  })
+
+  const throwingObserver = () => {
+    throwingObserverCalled = true
+    throw new Error('Failure')
+  }
+
+  const throwingDeepObserver = () => {
+    throwingDeepObserverCalled = true
+    throw new Error('Failure')
+  }
+
+  map.observe(throwingObserver)
+  map.observeDeep(throwingDeepObserver)
+
+  t.fails(() => {
+    map.set('y', '2')
+  })
+
+  t.assert(updateCalled)
+  t.assert(throwingObserverCalled)
+  t.assert(throwingDeepObserverCalled)
+
+  // check if it works again
+  updateCalled = false
+  throwingObserverCalled = false
+  throwingDeepObserverCalled = false
+  t.fails(() => {
+    map.set('z', '3')
+  })
+
+  t.assert(updateCalled)
+  t.assert(throwingObserverCalled)
+  t.assert(throwingDeepObserverCalled)
+
+  t.assert(map.get('z') === '3')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapEventHasCorrectValueWhenSettingAPrimitive = tc => {
+  const { users, map0 } = init(tc, { users: 3 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e
+  })
+  map0.set('stuff', 2)
+  t.compare(event.value, event.target.get(event.name))
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapEventHasCorrectValueWhenSettingAPrimitiveFromOtherUser = tc => {
+  const { users, map0, map1, testConnector } = init(tc, { users: 3 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e
+  })
+  map1.set('stuff', 2)
+  testConnector.flushAllMessages()
+  t.compare(event.value, event.target.get(event.name))
+  compare(users)
+}
+
+/**
+ * @type {Array<function(Doc,prng.PRNG):void>}
+ */
+const mapTransactions = [
+  function set (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    const value = prng.utf16String(gen)
+    user.getMap('map').set(key, value)
+  },
+  function setType (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    const type = prng.oneOf(gen, [new Y.Array(), new Y.Map()])
+    user.getMap('map').set(key, type)
+    if (type instanceof Y.Array) {
+      type.insert(0, [1, 2, 3, 4])
+    } else {
+      type.set('deepkey', 'deepvalue')
+    }
+  },
+  function _delete (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    user.getMap('map').delete(key)
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests10 = tc => {
+  applyRandomTests(tc, mapTransactions, 3)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests40 = tc => {
+  applyRandomTests(tc, mapTransactions, 40)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests42 = tc => {
+  applyRandomTests(tc, mapTransactions, 42)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests43 = tc => {
+  applyRandomTests(tc, mapTransactions, 43)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests44 = tc => {
+  applyRandomTests(tc, mapTransactions, 44)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests45 = tc => {
+  applyRandomTests(tc, mapTransactions, 45)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests46 = tc => {
+  applyRandomTests(tc, mapTransactions, 46)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests300 = tc => {
+  applyRandomTests(tc, mapTransactions, 300)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests400 = tc => {
+  applyRandomTests(tc, mapTransactions, 400)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests500 = tc => {
+  applyRandomTests(tc, mapTransactions, 500)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests600 = tc => {
+  applyRandomTests(tc, mapTransactions, 600)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests1000 = tc => {
+  applyRandomTests(tc, mapTransactions, 1000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests1800 = tc => {
+  applyRandomTests(tc, mapTransactions, 1800)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests5000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 5000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests10000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 10000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests100000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 100000)
+}
--- a/tests/y-text.tests.js
+++ b/tests/y-text.tests.js
@@ -0,0 +1,848 @@
+import * as Y from './testHelper.js'
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+import * as math from 'lib0/math'
+
+const { init, compare } = Y
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeltaAfterConcurrentFormatting = tc => {
+  const { text0, text1, testConnector } = init(tc, { users: 2 })
+  text0.insert(0, 'abcde')
+  testConnector.flushAllMessages()
+  text0.format(0, 3, { bold: true })
+  text1.format(2, 2, { bold: true })
+  let delta = null
+  text1.observe(event => {
+    delta = event.delta
+  })
+  testConnector.flushAllMessages()
+  t.compare(delta, [])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicInsertAndDelete = tc => {
+  const { users, text0 } = init(tc, { users: 2 })
+  let delta
+
+  text0.observe(event => {
+    delta = event.delta
+  })
+
+  text0.delete(0, 0)
+  t.assert(true, 'Does not throw when deleting zero elements with position 0')
+
+  text0.insert(0, 'abc')
+  t.assert(text0.toString() === 'abc', 'Basic insert works')
+  t.compare(delta, [{ insert: 'abc' }])
+
+  text0.delete(0, 1)
+  t.assert(text0.toString() === 'bc', 'Basic delete works (position 0)')
+  t.compare(delta, [{ delete: 1 }])
+
+  text0.delete(1, 1)
+  t.assert(text0.toString() === 'b', 'Basic delete works (position 1)')
+  t.compare(delta, [{ retain: 1 }, { delete: 1 }])
+
+  users[0].transact(() => {
+    text0.insert(0, '1')
+    text0.delete(0, 1)
+  })
+  t.compare(delta, [])
+
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicFormat = tc => {
+  const { users, text0 } = init(tc, { users: 2 })
+  let delta
+  text0.observe(event => {
+    delta = event.delta
+  })
+  text0.insert(0, 'abc', { bold: true })
+  t.assert(text0.toString() === 'abc', 'Basic insert with attributes works')
+  t.compare(text0.toDelta(), [{ insert: 'abc', attributes: { bold: true } }])
+  t.compare(delta, [{ insert: 'abc', attributes: { bold: true } }])
+  text0.delete(0, 1)
+  t.assert(text0.toString() === 'bc', 'Basic delete on formatted works (position 0)')
+  t.compare(text0.toDelta(), [{ insert: 'bc', attributes: { bold: true } }])
+  t.compare(delta, [{ delete: 1 }])
+  text0.delete(1, 1)
+  t.assert(text0.toString() === 'b', 'Basic delete works (position 1)')
+  t.compare(text0.toDelta(), [{ insert: 'b', attributes: { bold: true } }])
+  t.compare(delta, [{ retain: 1 }, { delete: 1 }])
+  text0.insert(0, 'z', { bold: true })
+  t.assert(text0.toString() === 'zb')
+  t.compare(text0.toDelta(), [{ insert: 'zb', attributes: { bold: true } }])
+  t.compare(delta, [{ insert: 'z', attributes: { bold: true } }])
+  // @ts-ignore
+  t.assert(text0._start.right.right.right.content.str === 'b', 'Does not insert duplicate attribute marker')
+  text0.insert(0, 'y')
+  t.assert(text0.toString() === 'yzb')
+  t.compare(text0.toDelta(), [{ insert: 'y' }, { insert: 'zb', attributes: { bold: true } }])
+  t.compare(delta, [{ insert: 'y' }])
+  text0.format(0, 2, { bold: null })
+  t.assert(text0.toString() === 'yzb')
+  t.compare(text0.toDelta(), [{ insert: 'yz' }, { insert: 'b', attributes: { bold: true } }])
+  t.compare(delta, [{ retain: 1 }, { retain: 1, attributes: { bold: null } }])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMultilineFormat = tc => {
+  const ydoc = new Y.Doc()
+  const testText = ydoc.getText('test')
+  testText.insert(0, 'Test\nMulti-line\nFormatting')
+  testText.applyDelta([
+    { retain: 4, attributes: { bold: true } },
+    { retain: 1 }, // newline character
+    { retain: 10, attributes: { bold: true } },
+    { retain: 1 }, // newline character
+    { retain: 10, attributes: { bold: true } }
+  ])
+  t.compare(testText.toDelta(), [
+    { insert: 'Test', attributes: { bold: true } },
+    { insert: '\n' },
+    { insert: 'Multi-line', attributes: { bold: true } },
+    { insert: '\n' },
+    { insert: 'Formatting', attributes: { bold: true } }
+  ])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testNotMergeEmptyLinesFormat = tc => {
+  const ydoc = new Y.Doc()
+  const testText = ydoc.getText('test')
+  testText.applyDelta([
+    { insert: 'Text' },
+    { insert: '\n', attributes: { title: true } },
+    { insert: '\nText' },
+    { insert: '\n', attributes: { title: true } }
+  ])
+  t.compare(testText.toDelta(), [
+    { insert: 'Text' },
+    { insert: '\n', attributes: { title: true } },
+    { insert: '\nText' },
+    { insert: '\n', attributes: { title: true } }
+  ])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetDeltaWithEmbeds = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.applyDelta([{
+    insert: { linebreak: 's' }
+  }])
+  t.compare(text0.toDelta(), [{
+    insert: { linebreak: 's' }
+  }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTypesAsEmbed = tc => {
+  const { text0, text1, testConnector } = init(tc, { users: 2 })
+  text0.applyDelta([{
+    insert: new Y.YMap([['key', 'val']])
+  }])
+  t.compare(text0.toDelta()[0].insert.toJSON(), { key: 'val' })
+  let firedEvent = false
+  text1.observe(event => {
+    const d = event.delta
+    t.assert(d.length === 1)
+    t.compare(d.map(x => /** @type {Y.AbstractType<any>} */ (x.insert).toJSON()), [{ key: 'val' }])
+    firedEvent = true
+  })
+  testConnector.flushAllMessages()
+  const delta = text1.toDelta()
+  t.assert(delta.length === 1)
+  t.compare(delta[0].insert.toJSON(), { key: 'val' })
+  t.assert(firedEvent, 'fired the event observer containing a Type-Embed')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSnapshot = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  const doc0 = /** @type {Y.Doc} */ (text0.doc)
+  doc0.gc = false
+  text0.applyDelta([{
+    insert: 'abcd'
+  }])
+  const snapshot1 = Y.snapshot(doc0)
+  text0.applyDelta([{
+    retain: 1
+  }, {
+    insert: 'x'
+  }, {
+    delete: 1
+  }])
+  const snapshot2 = Y.snapshot(doc0)
+  text0.applyDelta([{
+    retain: 2
+  }, {
+    delete: 3
+  }, {
+    insert: 'x'
+  }, {
+    delete: 1
+  }])
+  const state1 = text0.toDelta(snapshot1)
+  t.compare(state1, [{ insert: 'abcd' }])
+  const state2 = text0.toDelta(snapshot2)
+  t.compare(state2, [{ insert: 'axcd' }])
+  const state2Diff = text0.toDelta(snapshot2, snapshot1)
+  // @ts-ignore Remove userid info
+  state2Diff.forEach(v => {
+    if (v.attributes && v.attributes.ychange) {
+      delete v.attributes.ychange.user
+    }
+  })
+  t.compare(state2Diff, [{ insert: 'a' }, { insert: 'x', attributes: { ychange: { type: 'added' } } }, { insert: 'b', attributes: { ychange: { type: 'removed' } } }, { insert: 'cd' }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSnapshotDeleteAfter = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  const doc0 = /** @type {Y.Doc} */ (text0.doc)
+  doc0.gc = false
+  text0.applyDelta([{
+    insert: 'abcd'
+  }])
+  const snapshot1 = Y.snapshot(doc0)
+  text0.applyDelta([{
+    retain: 4
+  }, {
+    insert: 'e'
+  }])
+  const state1 = text0.toDelta(snapshot1)
+  t.compare(state1, [{ insert: 'abcd' }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testToJson = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.insert(0, 'abc', { bold: true })
+  t.assert(text0.toJSON() === 'abc', 'toJSON returns the unformatted text')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testToDeltaEmbedAttributes = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.insert(0, 'ab', { bold: true })
+  text0.insertEmbed(1, { image: 'imageSrc.png' }, { width: 100 })
+  const delta0 = text0.toDelta()
+  t.compare(delta0, [{ insert: 'a', attributes: { bold: true } }, { insert: { image: 'imageSrc.png' }, attributes: { width: 100 } }, { insert: 'b', attributes: { bold: true } }])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testToDeltaEmbedNoAttributes = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.insert(0, 'ab', { bold: true })
+  text0.insertEmbed(1, { image: 'imageSrc.png' })
+  const delta0 = text0.toDelta()
+  t.compare(delta0, [{ insert: 'a', attributes: { bold: true } }, { insert: { image: 'imageSrc.png' } }, { insert: 'b', attributes: { bold: true } }], 'toDelta does not set attributes key when no attributes are present')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testFormattingRemoved = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.insert(0, 'ab', { bold: true })
+  text0.delete(0, 2)
+  t.assert(Y.getTypeChildren(text0).length === 1)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testFormattingRemovedInMidText = tc => {
+  const { text0 } = init(tc, { users: 1 })
+  text0.insert(0, '1234')
+  text0.insert(2, 'ab', { bold: true })
+  text0.delete(2, 2)
+  t.assert(Y.getTypeChildren(text0).length === 3)
+}
+
+/**
+ * Reported in https://github.com/yjs/yjs/issues/344
+ *
+ * @param {t.TestCase} tc
+ */
+export const testFormattingDeltaUnnecessaryAttributeChange = tc => {
+  const { text0, text1, testConnector } = init(tc, { users: 2 })
+  text0.insert(0, '\n', {
+    PARAGRAPH_STYLES: 'normal',
+    LIST_STYLES: 'bullet'
+  })
+  text0.insert(1, 'abc', {
+    PARAGRAPH_STYLES: 'normal'
+  })
+  testConnector.flushAllMessages()
+  /**
+   * @type {Array<any>}
+   */
+  const deltas = []
+  text0.observe(event => {
+    deltas.push(event.delta)
+  })
+  text1.observe(event => {
+    deltas.push(event.delta)
+  })
+  text1.format(0, 1, { LIST_STYLES: 'number' })
+  testConnector.flushAllMessages()
+  const filteredDeltas = deltas.filter(d => d.length > 0)
+  t.assert(filteredDeltas.length === 2)
+  t.compare(filteredDeltas[0], [
+    { retain: 1, attributes: { LIST_STYLES: 'number' } }
+  ])
+  t.compare(filteredDeltas[0], filteredDeltas[1])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteAtRandomPositions = tc => {
+  const N = 100000
+  const { text0 } = init(tc, { users: 1 })
+  const gen = tc.prng
+
+  // create initial content
+  // let expectedResult = init
+  text0.insert(0, prng.word(gen, N / 2, N / 2))
+
+  // apply changes
+  for (let i = 0; i < N; i++) {
+    const pos = prng.uint32(gen, 0, text0.length)
+    if (prng.bool(gen)) {
+      const len = prng.uint32(gen, 1, 5)
+      const word = prng.word(gen, 0, len)
+      text0.insert(pos, word)
+      // expectedResult = expectedResult.slice(0, pos) + word + expectedResult.slice(pos)
+    } else {
+      const len = prng.uint32(gen, 0, math.min(3, text0.length - pos))
+      text0.delete(pos, len)
+      // expectedResult = expectedResult.slice(0, pos) + expectedResult.slice(pos + len)
+    }
+  }
+  // t.compareStrings(text0.toString(), expectedResult)
+  t.describe('final length', '' + text0.length)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testAppendChars = tc => {
+  const N = 10000
+  const { text0 } = init(tc, { users: 1 })
+
+  // apply changes
+  for (let i = 0; i < N; i++) {
+    text0.insert(text0.length, 'a')
+  }
+  t.assert(text0.length === N)
+}
+
+const largeDocumentSize = 100000
+
+const id = Y.createID(0, 0)
+const c = new Y.ContentString('a')
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBestCase = tc => {
+  const N = largeDocumentSize
+  const items = new Array(N)
+  t.measureTime('time to create two million items in the best case', () => {
+    const parent = /** @type {any} */ ({})
+    let prevItem = null
+    for (let i = 0; i < N; i++) {
+      /**
+       * @type {Y.Item}
+       */
+      const n = new Y.Item(Y.createID(0, 0), null, null, null, null, null, null, c)
+      // items.push(n)
+      items[i] = n
+      n.right = prevItem
+      n.rightOrigin = prevItem ? id : null
+      n.content = c
+      n.parent = parent
+      prevItem = n
+    }
+  })
+  const newArray = new Array(N)
+  t.measureTime('time to copy two million items to new Array', () => {
+    for (let i = 0; i < N; i++) {
+      newArray[i] = items[i]
+    }
+  })
+}
+
+const tryGc = () => {
+  // @ts-ignore
+  if (typeof global !== 'undefined' && global.gc) {
+    // @ts-ignore
+    global.gc()
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testLargeFragmentedDocument = tc => {
+  const itemsToInsert = largeDocumentSize
+  let update = /** @type {any} */ (null)
+  ;(() => {
+    const doc1 = new Y.Doc()
+    const text0 = doc1.getText('txt')
+    tryGc()
+    t.measureTime(`time to insert ${itemsToInsert} items`, () => {
+      doc1.transact(() => {
+        for (let i = 0; i < itemsToInsert; i++) {
+          text0.insert(0, '0')
+        }
+      })
+    })
+    tryGc()
+    t.measureTime('time to encode document', () => {
+      update = Y.encodeStateAsUpdateV2(doc1)
+    })
+    t.describe('Document size:', update.byteLength)
+  })()
+  ;(() => {
+    const doc2 = new Y.Doc()
+    tryGc()
+    t.measureTime(`time to apply ${itemsToInsert} updates`, () => {
+      Y.applyUpdateV2(doc2, update)
+    })
+  })()
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testIncrementalUpdatesPerformanceOnLargeFragmentedDocument = tc => {
+  const itemsToInsert = largeDocumentSize
+  const updates = /** @type {Array<Uint8Array>} */ ([])
+  ;(() => {
+    const doc1 = new Y.Doc()
+    doc1.on('update', update => {
+      updates.push(update)
+    })
+    const text0 = doc1.getText('txt')
+    tryGc()
+    t.measureTime(`time to insert ${itemsToInsert} items`, () => {
+      doc1.transact(() => {
+        for (let i = 0; i < itemsToInsert; i++) {
+          text0.insert(0, '0')
+        }
+      })
+    })
+    tryGc()
+  })()
+  ;(() => {
+    t.measureTime(`time to merge ${itemsToInsert} updates (differential updates)`, () => {
+      Y.mergeUpdates(updates)
+    })
+    tryGc()
+    t.measureTime(`time to merge ${itemsToInsert} updates (ydoc updates)`, () => {
+      const ydoc = new Y.Doc()
+      updates.forEach(update => {
+        Y.applyUpdate(ydoc, update)
+      })
+    })
+  })()
+}
+
+/**
+ * Splitting surrogates can lead to invalid encoded documents.
+ *
+ * https://github.com/yjs/yjs/issues/248
+ *
+ * @param {t.TestCase} tc
+ */
+export const testSplitSurrogateCharacter = tc => {
+  {
+    const { users, text0 } = init(tc, { users: 2 })
+    users[1].disconnect() // disconnecting forces the user to encode the split surrogate
+    text0.insert(0, '👾') // insert surrogate character
+    // split surrogate, which should not lead to an encoding error
+    text0.insert(1, 'hi!')
+    compare(users)
+  }
+  {
+    const { users, text0 } = init(tc, { users: 2 })
+    users[1].disconnect() // disconnecting forces the user to encode the split surrogate
+    text0.insert(0, '👾👾') // insert surrogate character
+    // partially delete surrogate
+    text0.delete(1, 2)
+    compare(users)
+  }
+  {
+    const { users, text0 } = init(tc, { users: 2 })
+    users[1].disconnect() // disconnecting forces the user to encode the split surrogate
+    text0.insert(0, '👾👾') // insert surrogate character
+    // formatting will also split surrogates
+    text0.format(1, 2, { bold: true })
+    compare(users)
+  }
+}
+
+/**
+ * Search marker bug https://github.com/yjs/yjs/issues/307
+ *
+ * @param {t.TestCase} tc
+ */
+export const testSearchMarkerBug1 = tc => {
+  const { users, text0, text1, testConnector } = init(tc, { users: 2 })
+
+  users[0].on('update', update => {
+    users[0].transact(() => {
+      Y.applyUpdate(users[0], update)
+    })
+  })
+  users[0].on('update', update => {
+    users[1].transact(() => {
+      Y.applyUpdate(users[1], update)
+    })
+  })
+
+  text0.insert(0, 'a_a')
+  testConnector.flushAllMessages()
+  text0.insert(2, 's')
+  testConnector.flushAllMessages()
+  text1.insert(3, 'd')
+  testConnector.flushAllMessages()
+  text0.delete(0, 5)
+  testConnector.flushAllMessages()
+  text0.insert(0, 'a_a')
+  testConnector.flushAllMessages()
+  text0.insert(2, 's')
+  testConnector.flushAllMessages()
+  text1.insert(3, 'd')
+  testConnector.flushAllMessages()
+  t.compareStrings(text0.toString(), text1.toString())
+  t.compareStrings(text0.toString(), 'a_sda')
+  compare(users)
+}
+
+/**
+ * Reported in https://github.com/yjs/yjs/pull/32
+ *
+ * @param {t.TestCase} tc
+ */
+export const testFormattingBug = async tc => {
+  const ydoc1 = new Y.Doc()
+  const ydoc2 = new Y.Doc()
+  const text1 = ydoc1.getText()
+  text1.insert(0, '\n\n\n')
+  text1.format(0, 3, { url: 'http://example.com' })
+  ydoc1.getText().format(1, 1, { url: 'http://docs.yjs.dev' })
+  ydoc2.getText().format(1, 1, { url: 'http://docs.yjs.dev' })
+  Y.applyUpdate(ydoc2, Y.encodeStateAsUpdate(ydoc1))
+  const text2 = ydoc2.getText()
+  const expectedResult = [
+    { insert: '\n', attributes: { url: 'http://example.com' } },
+    { insert: '\n', attributes: { url: 'http://docs.yjs.dev' } },
+    { insert: '\n', attributes: { url: 'http://example.com' } }
+  ]
+  t.compare(text1.toDelta(), expectedResult)
+  t.compare(text1.toDelta(), text2.toDelta())
+  console.log(text1.toDelta())
+}
+
+// RANDOM TESTS
+
+let charCounter = 0
+
+/**
+ * Random tests for pure text operations without formatting.
+ *
+ * @type Array<function(any,prng.PRNG):void>
+ */
+const textChanges = [
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // insert text
+    const ytext = y.getText('text')
+    const insertPos = prng.int32(gen, 0, ytext.length)
+    const text = charCounter++ + prng.word(gen)
+    const prevText = ytext.toString()
+    ytext.insert(insertPos, text)
+    t.compareStrings(ytext.toString(), prevText.slice(0, insertPos) + text + prevText.slice(insertPos))
+  },
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // delete text
+    const ytext = y.getText('text')
+    const contentLen = ytext.toString().length
+    const insertPos = prng.int32(gen, 0, contentLen)
+    const overwrite = math.min(prng.int32(gen, 0, contentLen - insertPos), 2)
+    const prevText = ytext.toString()
+    ytext.delete(insertPos, overwrite)
+    t.compareStrings(ytext.toString(), prevText.slice(0, insertPos) + prevText.slice(insertPos + overwrite))
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges5 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 5))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges30 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 30))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges40 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 40))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges50 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 50))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges70 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 70))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges90 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 90))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateTextChanges300 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, textChanges, 300))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+const marks = [
+  { bold: true },
+  { italic: true },
+  { italic: true, color: '#888' }
+]
+
+const marksChoices = [
+  undefined,
+  ...marks
+]
+
+/**
+ * Random tests for all features of y-text (formatting, embeds, ..).
+ *
+ * @type Array<function(any,prng.PRNG):void>
+ */
+const qChanges = [
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // insert text
+    const ytext = y.getText('text')
+    const insertPos = prng.int32(gen, 0, ytext.length)
+    const attrs = prng.oneOf(gen, marksChoices)
+    const text = charCounter++ + prng.word(gen)
+    ytext.insert(insertPos, text, attrs)
+  },
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // insert embed
+    const ytext = y.getText('text')
+    const insertPos = prng.int32(gen, 0, ytext.length)
+    if (prng.bool(gen)) {
+      ytext.insertEmbed(insertPos, { image: 'https://user-images.githubusercontent.com/5553757/48975307-61efb100-f06d-11e8-9177-ee895e5916e5.png' })
+    } else {
+      ytext.insertEmbed(insertPos, new Y.YMap([[prng.word(gen), prng.word(gen)]]))
+    }
+  },
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // delete text
+    const ytext = y.getText('text')
+    const contentLen = ytext.toString().length
+    const insertPos = prng.int32(gen, 0, contentLen)
+    const overwrite = math.min(prng.int32(gen, 0, contentLen - insertPos), 2)
+    ytext.delete(insertPos, overwrite)
+  },
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // format text
+    const ytext = y.getText('text')
+    const contentLen = ytext.toString().length
+    const insertPos = prng.int32(gen, 0, contentLen)
+    const overwrite = math.min(prng.int32(gen, 0, contentLen - insertPos), 2)
+    const format = prng.oneOf(gen, marks)
+    ytext.format(insertPos, overwrite, format)
+  },
+  /**
+   * @param {Y.Doc} y
+   * @param {prng.PRNG} gen
+   */
+  (y, gen) => { // insert codeblock
+    const ytext = y.getText('text')
+    const insertPos = prng.int32(gen, 0, ytext.toString().length)
+    const text = charCounter++ + prng.word(gen)
+    const ops = []
+    if (insertPos > 0) {
+      ops.push({ retain: insertPos })
+    }
+    ops.push({ insert: text }, { insert: '\n', format: { 'code-block': true } })
+    ytext.applyDelta(ops)
+  }
+]
+
+/**
+ * @param {any} result
+ */
+const checkResult = result => {
+  for (let i = 1; i < result.testObjects.length; i++) {
+    /**
+     * @param {any} d
+     */
+    const typeToObject = d => d.insert instanceof Y.AbstractType ? d.insert.toJSON() : d
+    const p1 = result.users[i].getText('text').toDelta().map(typeToObject)
+    const p2 = result.users[i].getText('text').toDelta().map(typeToObject)
+    t.compare(p1, p2)
+  }
+  // Uncomment this to find formatting-cleanup issues
+  // const cleanups = Y.cleanupYTextFormatting(result.users[0].getText('text'))
+  // t.assert(cleanups === 0)
+  return result
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges1 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, qChanges, 1))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges2 = tc => {
+  const { users } = checkResult(Y.applyRandomTests(tc, qChanges, 2))
+  const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+  t.assert(cleanups === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges2Repeat = tc => {
+  for (let i = 0; i < 1000; i++) {
+    const { users } = checkResult(Y.applyRandomTests(tc, qChanges, 2))
+    const cleanups = Y.cleanupYTextFormatting(users[0].getText('text'))
+    t.assert(cleanups === 0)
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges3 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 3))
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges30 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 30))
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges40 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 40))
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges70 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 70))
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges100 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 100))
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGenerateQuillChanges300 = tc => {
+  checkResult(Y.applyRandomTests(tc, qChanges, 300))
+}
--- a/tests/y-xml.tests.js
+++ b/tests/y-xml.tests.js
@@ -0,0 +1,185 @@
+import { init, compare } from './testHelper.js'
+import * as Y from '../src/index.js'
+
+import * as t from 'lib0/testing'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetProperty = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  xml0.setAttribute('height', '10')
+  t.assert(xml0.getAttribute('height') === '10', 'Simple set+get works')
+  testConnector.flushAllMessages()
+  t.assert(xml1.getAttribute('height') === '10', 'Simple set+get works (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testHasProperty = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  xml0.setAttribute('height', '10')
+  t.assert(xml0.hasAttribute('height'), 'Simple set+has works')
+  testConnector.flushAllMessages()
+  t.assert(xml1.hasAttribute('height'), 'Simple set+has works (remote)')
+
+  xml0.removeAttribute('height')
+  t.assert(!xml0.hasAttribute('height'), 'Simple set+remove+has works')
+  testConnector.flushAllMessages()
+  t.assert(!xml1.hasAttribute('height'), 'Simple set+remove+has works (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEvents = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let event
+  /**
+   * @type {any}
+   */
+  let remoteEvent
+  xml0.observe(e => {
+    event = e
+  })
+  xml1.observe(e => {
+    remoteEvent = e
+  })
+  xml0.setAttribute('key', 'value')
+  t.assert(event.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on updated key')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on updated key (remote)')
+  // check attributeRemoved
+  xml0.removeAttribute('key')
+  t.assert(event.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on removed attribute')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on removed attribute (remote)')
+  xml0.insert(0, [new Y.XmlText('some text')])
+  t.assert(event.childListChanged, 'YXmlEvent.childListChanged on inserted element')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.childListChanged, 'YXmlEvent.childListChanged on inserted element (remote)')
+  // test childRemoved
+  xml0.delete(0)
+  t.assert(event.childListChanged, 'YXmlEvent.childListChanged on deleted element')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.childListChanged, 'YXmlEvent.childListChanged on deleted element (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTreewalker = tc => {
+  const { users, xml0 } = init(tc, { users: 3 })
+  const paragraph1 = new Y.XmlElement('p')
+  const paragraph2 = new Y.XmlElement('p')
+  const text1 = new Y.XmlText('init')
+  const text2 = new Y.XmlText('text')
+  paragraph1.insert(0, [text1, text2])
+  xml0.insert(0, [paragraph1, paragraph2, new Y.XmlElement('img')])
+  const allParagraphs = xml0.querySelectorAll('p')
+  t.assert(allParagraphs.length === 2, 'found exactly two paragraphs')
+  t.assert(allParagraphs[0] === paragraph1, 'querySelectorAll found paragraph1')
+  t.assert(allParagraphs[1] === paragraph2, 'querySelectorAll found paragraph2')
+  t.assert(xml0.querySelector('p') === paragraph1, 'querySelector found paragraph1')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYtextAttributes = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = /** @type {Y.XmlText} */ (ydoc.get('', Y.XmlText))
+  ytext.observe(event => {
+    t.compare(event.changes.keys.get('test'), { action: 'add', oldValue: undefined })
+  })
+  ytext.setAttribute('test', 42)
+  t.compare(ytext.getAttribute('test'), 42)
+  t.compare(ytext.getAttributes(), { test: 42 })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSiblings = tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText()
+  const second = new Y.XmlElement('p')
+  yxml.insert(0, [first, second])
+  t.assert(first.nextSibling === second)
+  t.assert(second.prevSibling === first)
+  t.assert(first.parent === yxml)
+  t.assert(yxml.parent === null)
+  t.assert(yxml.firstChild === first)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertafter = tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText()
+  const second = new Y.XmlElement('p')
+  const third = new Y.XmlElement('p')
+
+  const deepsecond1 = new Y.XmlElement('span')
+  const deepsecond2 = new Y.XmlText()
+  second.insertAfter(null, [deepsecond1])
+  second.insertAfter(deepsecond1, [deepsecond2])
+
+  yxml.insertAfter(null, [first, second])
+  yxml.insertAfter(second, [third])
+
+  t.assert(yxml.length === 3)
+  t.assert(second.get(0) === deepsecond1)
+  t.assert(second.get(1) === deepsecond2)
+
+  t.compareArrays(yxml.toArray(), [first, second, third])
+
+  t.fails(() => {
+    const el = new Y.XmlElement('p')
+    el.insertAfter(deepsecond1, [new Y.XmlText()])
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testClone = tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText('text')
+  const second = new Y.XmlElement('p')
+  const third = new Y.XmlElement('p')
+  yxml.push([first, second, third])
+  t.compareArrays(yxml.toArray(), [first, second, third])
+
+  const cloneYxml = yxml.clone()
+  ydoc.getArray('copyarr').insert(0, [cloneYxml])
+  t.assert(cloneYxml.length === 3)
+  t.compare(cloneYxml.toJSON(), yxml.toJSON())
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testFormattingBug = tc => {
+  const ydoc = new Y.Doc()
+  const yxml = /** @type {Y.XmlText} */ (ydoc.get('', Y.XmlText))
+  const delta = [
+    { insert: 'A', attributes: { em: {}, strong: {} } },
+    { insert: 'B', attributes: { em: {} } },
+    { insert: 'C', attributes: { em: {}, strong: {} } }
+  ]
+  yxml.applyDelta(delta)
+  t.compare(yxml.toDelta(), delta)
+}
--- a/tsconfig.json
+++ b/tsconfig.json
@@ -0,0 +1,64 @@
+{
+  "compilerOptions": {
+    /* Basic Options */
+    "target": "es2018",
+    "lib": ["es2018", "dom"],                             /* Specify library files to be included in the compilation. */
+    "allowJs": true,                       /* Allow javascript files to be compiled. */
+    "checkJs": true,                       /* Report errors in .js files. */
+    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
+    "declaration": true,                   /* Generates corresponding '.d.ts' file. */
+    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
+    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
+    // "outFile": "./dist/yjs.js",                       /* Concatenate and emit output to single file. */
+    "outDir": "./dist",                        /* Redirect output structure to the directory. */
+    "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
+    // "composite": true,                     /* Enable project compilation */
+    // "removeComments": true,                /* Do not emit comments to output. */
+    // "noEmit": true,                        /* Do not emit outputs. */
+    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
+    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
+    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */
+
+    /* Strict Type-Checking Options */
+    "strict": true,                           /* Enable all strict type-checking options. */
+    "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
+    "emitDeclarationOnly": true,
+    // "strictNullChecks": true,              /* Enable strict null checks. */
+    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
+    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
+    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
+    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */
+
+    /* Additional Checks */
+    // "noUnusedLocals": true,                /* Report errors on unused locals. */
+    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
+    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
+    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */
+
+    /* Module Resolution Options */
+    "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
+    "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
+    "paths": {
+      "yjs": ["./src/index.js"]
+    },                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
+    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
+    // "typeRoots": [],                       /* List of folders to include type definitions from. */
+    // "types": [],                           /* Type declaration files to be included in compilation. */
+    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
+    "esModuleInterop": true,                   /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
+    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */
+
+    /* Source Map Options */
+    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
+    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
+    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
+    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */
+
+    /* Experimental Options */
+    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
+    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
+    // "maxNodeModuleJsDepth": 0,
+    // "types": ["./src/utils/typedefs.js"]
+  },
+  "include": ["./src/**/*.js", "./tests/**/*.js"]
+}