13.0.6

bump lib0 to fix critical encoding issue in safari
change client id when duplicate content is detected
2020-05-08 14:50:53 +02:00 · 2020-05-08 14:49:50 +02:00 · 2020-05-03 16:10:58 +02:00 · 2020-04-26 13:24:18 +02:00 · 2020-04-17 02:02:09 +02:00 · 2020-04-15 20:50:29 +02:00
102 changed files with 12883 additions and 31625 deletions
--- a/.babelrc
+++ b/.babelrc
@@ -1,12 +0,0 @@
-{
-  "presets": [
-    ["latest", {
-      "es2015": {
-        "modules": false
-      }
-    }]
-  ],
-  "plugins": [
-    "external-helpers"
-  ]
-}
--- a/.flowconfig
+++ b/.flowconfig
@@ -1,12 +0,0 @@
-[ignore]
-.*/node_modules/.*
-.*/dist/.*
-.*/build/.*
-
-[include]
-./src/
-
-[libs]
-./declarations/
-
-[options]
--- a/.github/FUNDING.yml
+++ b/.github/FUNDING.yml
@@ -0,0 +1,12 @@
+# These are supported funding model platforms
+
+github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+patreon: dmonad
+open_collective: # Replace with a single Open Collective username
+ko_fi: # Replace with a single Ko-fi username
+tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
+community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
+liberapay: # Replace with a single Liberapay username
+issuehunt: # Replace with a single IssueHunt username
+otechie: # Replace with a single Otechie username
+custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']
--- 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: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npm run lint
+    - run: npm run test-extensive
+      env:
+        CI: true
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 node_modules
-bower_components
-/y.*
+dist
+.vscode
+docs
--- a/.jsdoc.json
+++ b/.jsdoc.json
@@ -0,0 +1,50 @@
+{
+  "sourceType": "module",
+  "tags": {
+    "allowUnknownTags": true,
+    "dictionaries": ["jsdoc"]
+  },
+  "source": {
+    "include": ["./src"],
+    "includePattern": ".js$"
+  },
+  "plugins": [
+    "plugins/markdown"
+  ],
+  "templates": {
+    "referenceTitle": "Yjs",
+    "disableSort": false,
+    "useCollapsibles": true,
+    "collapse": true,
+    "resources": {
+      "yjs.dev": "Yjs website"
+    },
+    "logo": {
+      "url": "https://user-images.githubusercontent.com/5553757/48975307-61efb100-f06d-11e8-9177-ee895e5916e5.png",
+      "width": "162px",
+      "height": "162px",
+      "link": "/"
+    },
+    "tabNames": {
+      "api": "API",
+      "tutorials": "Examples"
+    },
+    "footerText": "Shared Editing",
+    "css": [
+      "./style.css"
+    ],
+    "default": {
+      "staticFiles": {
+          "include": ["examples/"]
+      }
+    }
+  },
+  "opts": {
+    "destination": "./docs/",
+    "encoding": "utf8",
+    "private": false,
+    "recurse": true,
+    "template": "./node_modules/tui-jsdoc-template",
+    "tutorials": "./examples"
+  }
+}
--- a/.markdownlint.json
+++ b/.markdownlint.json
@@ -0,0 +1,4 @@
+{
+  "default": true,
+  "no-inline-html": false
+}
--- a/README.md
+++ b/README.md
--- a/examples/ace/index.html
+++ b/examples/ace/index.html
@@ -1,32 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-    <style type="text/css" media="screen">
-    #aceContainer {
-        position: absolute;
-        top: 0;
-        right: 0;
-        bottom: 0;
-        left: 0;
-    }
-    .inserted {
-      position:absolute;
-      z-index:20;
-      background-color: #FFC107;
-    }
-    .deleted {
-      position:absolute;
-      z-index:20;
-      background-color: #FFC107;
-    }
-    </style>
-  </head>
-  <body>
-
-    <div id="aceContainer"></div>
-    <script src="../bower_components/yjs/y.js"></script>
-    <script src="../bower_components/ace-builds/src/ace.js"></script>
-
-    <script src="./index.js"></script>
-  </body>
-</html>
--- a/examples/ace/index.js
+++ b/examples/ace/index.js
@@ -1,24 +0,0 @@
-/* global Y, ace */
-
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'ace-example'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    ace: 'Text' // y.share.textarea is of type Y.Text
-  }
-}).then(function (y) {
-  window.yAce = y
-
-  // bind the textarea to a shared text element
-  var editor = ace.edit('aceContainer')
-  editor.setTheme('ace/theme/chrome')
-  editor.getSession().setMode('ace/mode/javascript')
-
-  y.share.ace.bindAce(editor)
-})
--- a/examples/bower.json
+++ b/examples/bower.json
@@ -1,29 +0,0 @@
-{
-  "name": "yjs-examples",
-  "version": "0.0.0",
-  "homepage": "y-js.org",
-  "authors": [
-    "Kevin Jahns <kevin.jahns@rwth-aachen.de>"
-  ],
-  "description": "Examples for Yjs",
-  "license": "MIT",
-  "ignore": [],
-  "dependencies": {
-    "yjs": "latest",
-    "y-array": "latest",
-    "y-map": "latest",
-    "y-memory": "latest",
-    "y-richtext": "latest",
-    "y-webrtc": "latest",
-    "y-websockets-client": "latest",
-    "y-text": "latest",
-    "y-indexeddb": "latest",
-    "y-xml": "latest",
-    "quill": "^1.0.0-rc.2",
-    "ace": "~1.2.3",
-    "ace-builds": "~1.2.3",
-    "jquery": "~2.2.2",
-    "d3": "^3.5.16",
-    "codemirror": "^5.25.0"
-  }
-}
--- a/examples/chat/index.html
+++ b/examples/chat/index.html
@@ -1,18 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <body>
-    <style>
-      #chat p span {
-        color: blue;
-      }
-    </style>
-    <div id="chat"></div>
-    <form id="chatform">
-      <input name="username" type="text" style="width:15%;">
-      <input name="message" type="text" style="width:60%;">
-      <input type="submit" value="Send">
-    </form>
-    <script src="../bower_components/yjs/y.js"></script>
-    <script src="./index.js"></script>
-  </body>
-</html>
--- a/examples/chat/index.js
+++ b/examples/chat/index.js
@@ -1,73 +0,0 @@
-/* global Y, chat */
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'chat-example'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    chat: 'Array'
-  }
-}).then(function (y) {
-  window.yChat = y
-  // This functions inserts a message at the specified position in the DOM
-  function appendMessage (message, position) {
-    var p = document.createElement('p')
-    var uname = document.createElement('span')
-    uname.appendChild(document.createTextNode(message.username + ': '))
-    p.appendChild(uname)
-    p.appendChild(document.createTextNode(message.message))
-    document.querySelector('#chat').insertBefore(p, chat.children[position] || null)
-  }
-  // This function makes sure that only 7 messages exist in the chat history.
-  // The rest is deleted
-  function cleanupChat () {
-    if (y.share.chat.length > 7) {
-      y.share.chat.delete(0, y.chat.length - 7)
-    }
-  }
-  // Insert the initial content
-  y.share.chat.toArray().forEach(appendMessage)
-  cleanupChat()
-
-  // whenever content changes, make sure to reflect the changes in the DOM
-  y.share.chat.observe(function (event) {
-    if (event.type === 'insert') {
-      for (let i = 0; i < event.length; i++) {
-        appendMessage(event.values[i], event.index + i)
-      }
-    } else if (event.type === 'delete') {
-      for (let i = 0; i < event.length; i++) {
-        chat.children[event.index].remove()
-      }
-    }
-    // concurrent insertions may result in a history > 7, so cleanup here
-    cleanupChat()
-  })
-  document.querySelector('#chatform').onsubmit = function (event) {
-    // the form is submitted
-    var message = {
-      username: this.querySelector('[name=username]').value,
-      message: this.querySelector('[name=message]').value
-    }
-    if (message.username.length > 0 && message.message.length > 0) {
-      if (y.share.chat.length > 6) {
-        // If we are goint to insert the 8th element, make sure to delete first.
-        y.share.chat.delete(0)
-      }
-      // Here we insert a message in the shared chat type.
-      // This will call the observe function (see line 40)
-      // and reflect the change in the DOM
-      y.share.chat.push([message])
-      this.querySelector('[name=message]').value = ''
-    }
-    // Do not send this form!
-    event.preventDefault()
-    return false
-  }
-})
--- a/examples/codemirror/index.html
+++ b/examples/codemirror/index.html
@@ -1,23 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-  </head>
-  <body>
-    <div id="codeMirrorContainer"></div>
-
-    <script src="../bower_components/yjs/y.js"></script>
-    <script src="../bower_components/codemirror/lib/codemirror.js"></script>
-    <script src="../bower_components/codemirror/mode/javascript/javascript.js"></script>
-    <link rel="stylesheet" href="../bower_components/codemirror/lib/codemirror.css">
-    <style>
-      .CodeMirror {
-        position: fixed;
-        top: 0;
-        left: 0;
-        height: 100%;
-        width: 100%;
-      }
-    </style>
-    <script src="./index.js"></script>
-  </body>
-</html>
--- a/examples/codemirror/index.js
+++ b/examples/codemirror/index.js
@@ -1,24 +0,0 @@
-/* global Y, CodeMirror */
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'codemirror-example'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    codemirror: 'Text' // y.share.codemirror is of type Y.Text
-  }
-}).then(function (y) {
-  window.yCodeMirror = y
-
-  var editor = CodeMirror(document.querySelector('#codeMirrorContainer'), {
-    mode: 'javascript',
-    lineNumbers: true
-  })
-  y.share.codemirror.bindCodeMirror(editor)
-})
--- a/examples/drawing/index.html
+++ b/examples/drawing/index.html
@@ -1,19 +0,0 @@
-<!DOCTYPE html>
-<html>
-<body>
-  <style>
-    path {
-      fill: none;
-      stroke: blue;
-      stroke-width: 1px;
-      stroke-linejoin: round;
-      stroke-linecap: round;
-    }
-  </style>
-  <button type="button" id="clearDrawingCanvas">Clear Drawing</button>
-  <svg id="drawingCanvas" viewbox="0 0 100 100" width="100%"></svg>
-  <script src="../bower_components/yjs/y.js"></script>
-  <script src="../bower_components/d3/d3.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/examples/drawing/index.js
+++ b/examples/drawing/index.js
@@ -1,84 +0,0 @@
-/* globals Y, d3 */
-'strict mode'
-
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'drawing-example'
-    // url: 'localhost:1234'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    drawing: 'Array'
-  }
-}).then(function (y) {
-  window.yDrawing = y
-  var drawing = y.share.drawing
-  var renderPath = d3.svg.line()
-    .x(function (d) { return d[0] })
-    .y(function (d) { return d[1] })
-    .interpolate('basis')
-
-  var svg = d3.select('#drawingCanvas')
-    .call(d3.behavior.drag()
-      .on('dragstart', dragstart)
-      .on('drag', drag)
-      .on('dragend', dragend))
-
-  // create line from a shared array object and update the line when the array changes
-  function drawLine (yarray) {
-    var line = svg.append('path').datum(yarray.toArray())
-    line.attr('d', renderPath)
-    yarray.observe(function (event) {
-      // we only implement insert events that are appended to the end of the array
-      event.values.forEach(function (value) {
-        line.datum().push(value)
-      })
-      line.attr('d', renderPath)
-    })
-  }
-  // call drawLine every time an array is appended
-  y.share.drawing.observe(function (event) {
-    if (event.type === 'insert') {
-      event.values.forEach(drawLine)
-    } else {
-      // just remove all elements (thats what we do anyway)
-      svg.selectAll('path').remove()
-    }
-  })
-  // draw all existing content
-  for (var i = 0; i < drawing.length; i++) {
-    drawLine(drawing.get(i))
-  }
-
-  // clear canvas on request
-  document.querySelector('#clearDrawingCanvas').onclick = function () {
-    drawing.delete(0, drawing.length)
-  }
-
-  var sharedLine = null
-  function dragstart () {
-    drawing.insert(drawing.length, [Y.Array])
-    sharedLine = drawing.get(drawing.length - 1)
-  }
-
-  // After one dragged event is recognized, we ignore them for 33ms.
-  var ignoreDrag = null
-  function drag () {
-    if (sharedLine != null && ignoreDrag == null) {
-      ignoreDrag = window.setTimeout(function () {
-        ignoreDrag = null
-      }, 33)
-      sharedLine.push([d3.mouse(this)])
-    }
-  }
-
-  function dragend () {
-    sharedLine = null
-    window.clearTimeout(ignoreDrag)
-    ignoreDrag = null
-  }
-})
--- a/examples/jigsaw/index.html
+++ b/examples/jigsaw/index.html
@@ -1,23 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-  <style type="text/css">
-    .draggable {
-      cursor: move;
-    }
-  </style>
-</head>
-<body>
-  <svg id="puzzle-example" width="100%" viewBox="0 0 800 800">
-    <g>
-      <path d="M 311.76636,154.23389 C 312.14136,171.85693 318.14087,184.97998 336.13843,184.23047 C 354.13647,183.48047 351.88647,180.48096 354.88599,178.98096 C 357.8855,177.48096 368.38452,170.35693 380.00806,169.98193 C 424.61841,168.54297 419.78296,223.6001 382.25757,223.6001 C 377.75806,223.6001 363.51001,219.10107 356.38599,211.97656 C 349.26196,204.85254 310.64185,207.10254 314.76636,236.34863 C 316.34888,247.5708 324.08374,267.90723 324.84595,286.23486 C 325.29321,296.99414 323.17603,307.00635 321.58911,315.6377 C 360.11353,305.4585 367.73462,304.30518 404.00513,312.83936 C 410.37915,314.33887 436.62573,310.21436 421.25269,290.3418 C 405.87964,270.46924 406.25464,248.34717 417.12817,240.84814 C 428.00171,233.34912 446.74976,228.84961 457.99829,234.09912 C 469.24683,239.34814 484.61987,255.84619 475.24585,271.59424 C 465.87231,287.34229 452.74878,290.7168 456.49829,303.84033 C 460.2478,316.96387 479.74536,320.33838 500.74292,321.83789 C 509.70142,322.47803 527.97192,323.28467 542.10864,320.12939 C 549.91821,318.38672 556.92212,315.89502 562.46753,313.56396 C 561.40796,277.80664 560.84888,245.71729 560.3606,241.97314 C 558.85278,230.41455 542.49536,217.28564 525.86499,223.2251 C 520.61548,225.1001 519.86548,231.84912 505.24243,232.59912 C 444.92798,235.69238 462.06958,143.26709 525.86499,180.48096 C 539.52759,188.45068 575.19409,190.7583 570.10913,156.85889 C 567.85962,141.86035 553.98608,102.86523 553.98608,102.86523 C 553.98608,102.86523 477.23755,111.82227 451.99878,91.991699 C 441.50024,83.74292 444.87476,69.494629 449.37427,61.245605 C 453.87378,52.996582 465.12231,46.622559 464.74731,36.123779 C 463.02563,-12.086426 392.96704,-10.902832 396.5061,36.873535 C 397.25562,46.997314 406.62964,52.621582 410.75415,60.495605 C 420.00757,78.161377 405.50024,96.073486 384.50757,99.490723 C 377.36206,100.65381 349.17505,102.65332 320.39429,102.23486 C 319.677,102.22461 318.95923,102.21143 318.24194,102.19775 C 315.08423,120.9751 311.55688,144.39697 311.76636,154.23389 z " style="fill:#f2c569;stroke:#000000" id="path2502"/>
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-      <path d="M 240.52563,141.86035 C 257.60327,159.6499 243.94507,188.68799 214.65356,190.22949 C 185.09448,191.78516 164.66675,157.17822 190.28589,136.61621 C 200.49585,128.42139 198.05786,114.12158 179.78296,106.98975 C 154.4187,97.091553 90.54419,107.73975 90.54419,107.73975 C 90.54419,107.73975 100.88794,135.11328 101.41772,168.48242 C 101.79272,192.104 68.796875,189.47949 63.172607,186.85498 C 57.54834,184.23047 45.924805,173.73145 37.675781,173.73145 C -14.411865,173.73145 -10.013184,245.84375 39.925537,232.22412 C 48.174316,229.97461 56.42334,220.97559 68.796875,222.47559 C 81.17041,223.9751 87.544434,232.59912 87.544434,246.09766 C 87.544434,252.51709 87.0354,281.24268 86.340576,312.87012 C 119.15894,313.67676 160.60962,314.46582 170.03442,313.58887 C 186.15698,312.08936 195.90601,301.59033 188.40698,293.3418 C 180.90796,285.09277 156.16089,256.59619 179.03296,239.34814 C 201.90503,222.10059 235.65112,231.84912 239.77563,247.22217 C 243.90015,262.59521 240.52563,273.46924 234.90112,279.09326 C 229.27661,284.71777 210.52905,298.96582 221.40259,308.71484 C 232.27661,318.46338 263.77222,330.83691 302.39282,320.71338 C 309.58862,318.82715 315.92114,317.13525 321.58911,315.6377 C 323.17603,307.00635 325.29321,296.99414 324.84595,286.23486 C 324.08374,267.90723 316.34888,247.5708 314.76636,236.34863 C 310.64185,207.10254 349.26196,204.85254 356.38599,211.97656 C 363.51001,219.10107 377.75806,223.6001 382.25757,223.6001 C 419.78296,223.6001 424.61841,168.54297 380.00806,169.98193 C 368.38452,170.35693 357.8855,177.48096 354.88599,178.98096 C 351.88647,180.48096 354.13647,183.48047 336.13843,184.23047 C 318.14087,184.97998 312.14136,171.85693 311.76636,154.23389 C 311.55688,144.39697 315.08423,120.9751 318.24194,102.19775 C 290.37524,101.67725 262.46069,98.968262 254.39868,97.991211 C 233.38013,95.443359 217.17456,117.53662 240.52563,141.86035 z " style="fill:#bebcdb;stroke:#000000" id="path2506"/>
-      <path d="M 325.63989,452.69678 C 317.92163,423.11035 287.36353,445.9126 268.64673,447.82227 C 250.27417,449.69727 239.77563,436.57373 239.77563,419.32568 C 239.77563,402.07812 254.02368,395.70361 265.27222,394.5791 C 276.52075,393.4541 282.14526,396.45361 297.89331,407.32715 C 313.64136,418.20117 326.3894,399.45313 327.8894,392.7041 C 329.3894,385.95508 320.76538,342.83545 320.01538,330.46191 C 319.75855,326.2207 320.56372,321.21484 321.58911,315.6377 C 315.92114,317.13525 309.58862,318.82715 302.39282,320.71338 C 263.77222,330.83691 232.27661,318.46338 221.40259,308.71484 C 210.52905,298.96582 229.27661,284.71777 234.90112,279.09326 C 240.52563,273.46924 243.90015,262.59521 239.77563,247.22217 C 235.65112,231.84912 201.90503,222.10059 179.03296,239.34814 C 156.16089,256.59619 180.90796,285.09277 188.40698,293.3418 C 195.90601,301.59033 186.15698,312.08936 170.03442,313.58887 C 160.60962,314.46582 119.15894,313.67676 86.340576,312.87012 C 85.573975,347.74561 84.581299,386.15088 83.794922,402.07812 C 82.295166,432.44922 109.29175,422.32568 115.66577,420.82568 C 122.04028,419.32568 126.16479,409.57715 143.03735,408.45215 C 185.9231,405.59326 186.09985,466.69629 144.16235,467.69482 C 128.41431,468.06982 113.79126,451.19678 108.16675,447.44727 C 102.54272,443.69775 87.919433,442.94775 83.794922,457.9458 C 82.01709,464.41113 78.118652,481.65137 78.098144,496.18994 C 78.071045,515.38037 82.295166,531.81201 82.295166,531.81201 C 82.295166,531.81201 105.54224,526.5625 149.41187,526.5625 C 193.28149,526.5625 199.65552,547.93506 194.78101,558.80859 C 189.90649,569.68213 181.28296,568.93213 179.40796,583.18066 C 172.7063,634.11133 253.34106,631.08203 249.14917,584.68018 C 247.96948,571.62354 237.16528,571.66699 232.27661,557.68359 C 222.17944,528.80273 244.64966,523.56299 257.39819,524.68799 C 263.59351,525.23437 290.95679,529.73389 320.75757,531.21582 C 321.22437,531.23877 321.69312,531.25928 322.16089,531.28125 C 326.09985,518.06592 329.95825,503.87646 330.1394,498.44092 C 330.51392,487.19238 330.1394,469.94434 325.63989,452.69678 z " style="fill:#d3ea9d;stroke:#000000" id="path2508"/>
-		</g>
-  </svg>
-  <script src="../bower_components/yjs/y.js"></script>
-  <script src="../bower_components/d3/d3.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/examples/jigsaw/index.js
+++ b/examples/jigsaw/index.js
@@ -1,74 +0,0 @@
-/* @flow */
-/* global Y, d3 */
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'Puzzle-example'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    piece1: 'Map',
-    piece2: 'Map',
-    piece3: 'Map',
-    piece4: 'Map'
-  }
-}).then(function (y) {
-  window.yJigsaw = y
-  var origin // mouse start position - translation of piece
-  var drag = d3.behavior.drag()
-    .on('dragstart', function (params) {
-      // get the translation of the element
-      var translation = d3
-        .select(this)
-        .attr('transform')
-        .slice(10, -1)
-        .split(',')
-        .map(Number)
-      // mouse coordinates
-      var mouse = d3.mouse(this.parentNode)
-      origin = {
-        x: mouse[0] - translation[0],
-        y: mouse[1] - translation[1]
-      }
-    })
-    .on('drag', function () {
-      var mouse = d3.mouse(this.parentNode)
-      var x = mouse[0] - origin.x // =^= mouse - mouse at dragstart + translation at dragstart
-      var y = mouse[1] - origin.y
-      d3.select(this).attr('transform', 'translate(' + x + ',' + y + ')')
-    })
-    .on('dragend', function (piece, i) {
-      // save the current translation of the puzzle piece
-      var mouse = d3.mouse(this.parentNode)
-      var x = mouse[0] - origin.x
-      var y = mouse[1] - origin.y
-      piece.set('translation', {x: x, y: y})
-    })
-
-  var data = [y.share.piece1, y.share.piece2, y.share.piece3, y.share.piece4]
-  var pieces = d3.select(document.querySelector('#puzzle-example')).selectAll('path').data(data)
-
-  pieces
-    .classed('draggable', true)
-    .attr('transform', function (piece) {
-      var translation = piece.get('translation') || {x: 0, y: 0}
-      return 'translate(' + translation.x + ',' + translation.y + ')'
-    }).call(drag)
-
-  data.forEach(function (piece) {
-    piece.observe(function () {
-      // whenever a property of a piece changes, update the translation of the pieces
-      pieces
-        .transition()
-        .attr('transform', function (piece) {
-          var translation = piece.get('translation') || {x: 0, y: 0}
-          return 'translate(' + translation.x + ',' + translation.y + ')'
-        })
-    })
-  })
-})
--- a/examples/monaco/index.html
+++ b/examples/monaco/index.html
@@ -1,24 +0,0 @@
-<!DOCTYPE html>
-<html>
-  <head>
-  </head>
-  <body>
-    <div id="monacoContainer"></div>
-    <style>
-      #monacoContainer {
-        position: fixed;
-        top: 0;
-        left: 0;
-        height: 100%;
-        width: 100%;
-      }
-    </style>
-    <script src="../bower_components/yjs/y.js"></script>
-    <script src="../bower_components/y-array/y-array.js"></script>
-    <script src="../bower_components/y-text/y-text.js"></script>
-    <script src="../bower_components/y-websockets-client/y-websockets-client.js"></script>
-    <script src="../bower_components/y-memory/y-memory.js"></script>
-    <script src="../node_modules/monaco-editor/min/vs/loader.js"></script>
-    <script src="./index.js"></script>
-  </body>
-</html>
--- a/examples/monaco/index.js
+++ b/examples/monaco/index.js
@@ -1,30 +0,0 @@
-/* global Y, monaco */
-
-require.config({ paths: { 'vs': '../node_modules/monaco-editor/min/vs' } })
-
-require(['vs/editor/editor.main'], function () {
-  // Initialize a shared object. This function call returns a promise!
-  Y({
-    db: {
-      name: 'memory'
-    },
-    connector: {
-      name: 'websockets-client',
-      room: 'monaco-example'
-    },
-    sourceDir: '/bower_components',
-    share: {
-      monaco: 'Text' // y.share.monaco is of type Y.Text
-    }
-  }).then(function (y) {
-    window.yMonaco = y
-
-    // Create Monaco editor
-    var editor = monaco.editor.create(document.getElementById('monacoContainer'), {
-      language: 'javascript'
-    })
-
-    // Bind to y.share.monaco
-    y.share.monaco.bindMonaco(editor)
-  })
-})
--- a/examples/package-lock.json
+++ b/examples/package-lock.json
--- a/examples/package.json
+++ b/examples/package.json
@@ -1,16 +0,0 @@
-{
-  "name": "examples",
-  "version": "0.0.0",
-  "description": "",
-  "author": "Kevin Jahns",
-  "license": "MIT",
-  "dependencies": {
-    "monaco-editor": "^0.8.3"
-  },
-  "devDependencies": {
-    "standard": "^10.0.2"
-  },
-  "standard": {
-    "ignore": ["bower_components"]
-  }
-}
--- a/examples/quill/index.html
+++ b/examples/quill/index.html
@@ -1,31 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-  <!-- quill does not include dist files! We are using the hosted version instead -->
-  <!--link rel="stylesheet" href="../bower_components/quill/dist/quill.snow.css" /-->
-  <link href="https://cdn.quilljs.com/1.0.4/quill.snow.css" rel="stylesheet">
-  <link href="//cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.css" rel="stylesheet">
-  <link href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.2.0/styles/monokai-sublime.min.css" rel="stylesheet">
-  <style>
-    #quill-container {
-      border: 1px solid gray;
-      box-shadow: 0px 0px 10px gray;
-    }
-  </style>
-</head>
-<body>
-  <div id="quill-container">
-    <div id="quill">
-    </div>
-  </div>
-
-  <script src="//cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.js" type="text/javascript"></script>
-  <script src="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.2.0/highlight.min.js" type="text/javascript"></script>
-  <script src="https://cdn.quilljs.com/1.0.4/quill.js"></script>
-  <!-- quill does not include dist files! We are using the hosted version instead (see above)
-  <script src="../bower_components/quill/dist/quill.js"></script>
-  -->
-  <script src="../bower_components/yjs/y.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/examples/quill/index.js
+++ b/examples/quill/index.js
@@ -1,39 +0,0 @@
-/* global Y, Quill */
-
-// initialize a shared object. This function call returns a promise!
-
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'richtext-example-quill-1.0-test'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    richtext: 'Richtext' // y.share.richtext is of type Y.Richtext
-  }
-}).then(function (y) {
-  window.yQuill = y
-
-  // create quill element
-  window.quill = new Quill('#quill', {
-    modules: {
-      formula: true,
-      syntax: true,
-      toolbar: [
-        [{ size: ['small', false, 'large', 'huge'] }],
-        ['bold', 'italic', 'underline'],
-        [{ color: [] }, { background: [] }],    // Snow theme fills in values
-        [{ script: 'sub' }, { script: 'super' }],
-        ['link', 'image'],
-        ['link', 'code-block'],
-        [{ list: 'ordered' }]
-      ]
-    },
-    theme: 'snow'
-  })
-  // bind quill to richtext type
-  y.share.richtext.bind(window.quill)
-})
--- a/examples/serviceworker/index.html
+++ b/examples/serviceworker/index.html
@@ -1,31 +0,0 @@
-<!DOCTYPE html>
-<html>
-<head>
-  <!-- quill does not include dist files! We are using the hosted version instead -->
-  <!--link rel="stylesheet" href="../bower_components/quill/dist/quill.snow.css" /-->
-  <link href="https://cdn.quilljs.com/1.0.4/quill.snow.css" rel="stylesheet">
-  <link href="//cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.css" rel="stylesheet">
-  <link href="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.2.0/styles/monokai-sublime.min.css" rel="stylesheet">
-  <style>
-    #quill-container {
-      border: 1px solid gray;
-      box-shadow: 0px 0px 10px gray;
-    }
-  </style>
-</head>
-<body>
-  <div id="quill-container">
-    <div id="quill">
-    </div>
-  </div>
-
-  <script src="//cdnjs.cloudflare.com/ajax/libs/KaTeX/0.5.1/katex.min.js" type="text/javascript"></script>
-  <script src="//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.2.0/highlight.min.js" type="text/javascript"></script>
-  <script src="https://cdn.quilljs.com/1.0.4/quill.js"></script>
-  <!-- quill does not include dist files! We are using the hosted version instead (see above)
-  <script src="../bower_components/quill/dist/quill.js"></script>
-  -->
-  <script src="../bower_components/yjs/y.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/examples/serviceworker/index.js
+++ b/examples/serviceworker/index.js
@@ -1,49 +0,0 @@
-/* global Y, Quill */
-
-// register yjs service worker
-if ('serviceWorker' in navigator) {
-  // Register service worker
-  // it is important to copy yjs-sw-template to the root directory!
-  navigator.serviceWorker.register('./yjs-sw-template.js').then(function (reg) {
-    console.log('Yjs service worker registration succeeded. Scope is ' + reg.scope)
-  }).catch(function (err) {
-    console.error('Yjs service worker registration failed with error ' + err)
-  })
-}
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'serviceworker',
-    room: 'ServiceWorkerExample2'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    richtext: 'Richtext' // y.share.richtext is of type Y.Richtext
-  }
-}).then(function (y) {
-  window.yServiceWorker = y
-
-  // create quill element
-  window.quill = new Quill('#quill', {
-    modules: {
-      formula: true,
-      syntax: true,
-      toolbar: [
-        [{ size: ['small', false, 'large', 'huge'] }],
-        ['bold', 'italic', 'underline'],
-        [{ color: [] }, { background: [] }],    // Snow theme fills in values
-        [{ script: 'sub' }, { script: 'super' }],
-        ['link', 'image'],
-        ['link', 'code-block'],
-        [{ list: 'ordered' }]
-      ]
-    },
-    theme: 'snow'
-  })
-  // bind quill to richtext type
-  y.share.richtext.bind(window.quill)
-})
--- a/examples/serviceworker/yjs-sw-template.js
+++ b/examples/serviceworker/yjs-sw-template.js
@@ -1,22 +0,0 @@
-/* eslint-env worker */
-
-// copy and modify this file
-
-self.DBConfig = {
-  name: 'indexeddb'
-}
-self.ConnectorConfig = {
-  name: 'websockets-client',
-  // url: '..',
-  options: {
-    jsonp: false
-  }
-}
-
-importScripts(
-  '/bower_components/yjs/y.js',
-  '/bower_components/y-memory/y-memory.js',
-  '/bower_components/y-indexeddb/y-indexeddb.js',
-  '/bower_components/y-websockets-client/y-websockets-client.js',
-  '/bower_components/y-serviceworker/yjs-sw-include.js'
-)
--- a/examples/textarea/index.html
+++ b/examples/textarea/index.html
@@ -1,12 +0,0 @@
-<!DOCTYPE html>
-<html>
-<body>
-  <textarea style="width:80%;" rows=40 id="textfield" autocomplete="off" autocorrect="off" autocapitalize="off" spellcheck="false"></textarea>
-  <script src="../../y.js"></script>
-  <script src="../../../y-array/y-array.js"></script>
-  <script src="../../../y-text/dist/y-text.js"></script>
-  <script src="../../../y-memory/y-memory.js"></script>
-  <script src="../../../y-websockets-client/y-websockets-client.js"></script>
-  <script src="./index.js"></script>
-</body>
-</html>
--- a/examples/textarea/index.js
+++ b/examples/textarea/index.js
@@ -1,23 +0,0 @@
-/* global Y */
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'Textarea-example-dev'
-    // url: '127.0.0.1:1234'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    textarea: 'Text' // y.share.textarea is of type Y.Text
-  }
-}).then(function (y) {
-  window.yTextarea = y
-
-  // bind the textarea to a shared text element
-  y.share.textarea.bind(document.getElementById('textfield'))
-  // thats it..
-})
--- a/examples/xml/index.html
+++ b/examples/xml/index.html
@@ -1,39 +0,0 @@
-<!DOCTYPE html>
-<html>
-</head>
-  <script src="../bower_components/yjs/y.js"></script>
-  <script src="../bower_components/jquery/dist/jquery.min.js"></script>
-  <script src="./index.js"></script>
-</head>
-<body>
-  <h1> Shared DOM Example </h1>
-  <p> Use native DOM function or jQuery to manipulate the shared DOM (window.sharedDom). </p>
-  <div class="command">
-    <button type="button">Execute</button>
-    <input type="text" value='$(sharedDom).append("<h3>Appended headline</h3>")' size="40"/>
-  </div>
-  <div class="command">
-    <button type="button">Execute</button>
-    <input type="text" value='$(sharedDom).attr("align","right")' size="40"/>
-  </div>
-  <div class="command">
-    <button type="button">Execute</button>
-    <input type="text" value='$(sharedDom).attr("style","color:blue;")' size="40"/>
-  </div>
-
-  <script>
-    var commands = document.querySelectorAll(".command");
-    Array.prototype.forEach.call(document.querySelectorAll('.command'), function (command) {
-      var execute = function(){
-        eval(command.querySelector("input").value);
-      }
-      command.querySelector("button").onclick = execute
-      $(command.querySelector("input")).keyup(function (e) {
-        if (e.keyCode == 13) {
-          execute()
-        }
-      })
-    })
-  </script>
-</body>
-</html>
--- a/examples/xml/index.js
+++ b/examples/xml/index.js
@@ -1,21 +0,0 @@
-/* global Y */
-
-// initialize a shared object. This function call returns a promise!
-Y({
-  db: {
-    name: 'memory'
-  },
-  connector: {
-    name: 'websockets-client',
-    room: 'Xml-example'
-  },
-  sourceDir: '/bower_components',
-  share: {
-    xml: 'Xml("p")' // y.share.xml is of type Y.Xml with tagname "p"
-  }
-}).then(function (y) {
-  window.yXml = y
-  // bind xml type to a dom, and put it in body
-  window.sharedDom = y.share.xml.getDom()
-  document.body.appendChild(window.sharedDom)
-})
--- a/package-lock.json
+++ b/package-lock.json
--- a/package.json
+++ b/package.json
@@ -1,66 +1,75 @@
 {
  "name": "yjs",
-  "version": "13.0.0-5",
-  "description": "A framework for real-time p2p shared editing on any data",
-  "main": "./y.node.js",
-  "browser": "./y.js",
-  "module": "./src/y.js",
+  "version": "13.0.6",
+  "description": "Shared Editing Library",
+  "main": "./dist/yjs.cjs",
+  "module": "./dist/yjs.mjs",
+  "types": "./dist/src/index.d.ts",
+  "sideEffects": false,
  "scripts": {
-    "test": "npm run lint",
-    "lint": "standard",
-    "dist": "rollup -c rollup.browser.js; rollup -c rollup.node.js",
-    "postversion": "npm run dist",
-    "postpublish": "tag-dist-files --overwrite-existing-tag"
+    "test": "npm run dist && node ./dist/tests.cjs --repitition-time 50",
+    "test-extensive": "npm run lint && npm run dist && node ./dist/tests.cjs --production --repitition-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 --repitition-time 1000",
+    "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"
  },
  "files": [
-    "y.*"
+    "dist/*",
+    "src/*",
+    "tests/*",
+    "docs/*"
  ],
+  "dictionaries": {
+    "doc": "docs",
+    "test": "tests"
+  },
  "standard": {
    "ignore": [
-      "/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": [
    "Yjs",
-    "OT",
-    "Collaboration",
-    "Synchronization",
-    "ShareJS",
-    "Coweb",
-    "Concurrency"
+    "CRDT",
+    "offline",
+    "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"
-  },
-  "homepage": "http://y-js.org",
-  "devDependencies": {
-    "babel-cli": "^6.24.1",
-    "babel-plugin-external-helpers": "^6.22.0",
-    "babel-plugin-transform-regenerator": "^6.24.1",
-    "babel-plugin-transform-runtime": "^6.23.0",
-    "babel-preset-latest": "^6.24.1",
-    "chance": "^1.0.9",
-    "concurrently": "^3.4.0",
-    "rollup-plugin-babel": "^2.7.1",
-    "rollup-plugin-commonjs": "^8.0.2",
-    "rollup-plugin-inject": "^2.0.0",
-    "rollup-plugin-multi-entry": "^2.0.1",
-    "rollup-plugin-node-resolve": "^3.0.0",
-    "rollup-plugin-uglify": "^1.0.2",
-    "rollup-regenerator-runtime": "^6.23.1",
-    "rollup-watch": "^3.2.2",
-    "standard": "^10.0.2",
-    "tag-dist-files": "^0.1.6"
+    "url": "https://github.com/yjs/yjs/issues"
  },
+  "homepage": "https://yjs.dev",
  "dependencies": {
-    "debug": "^2.6.8"
+    "lib0": "^0.2.26"
+  },
+  "devDependencies": {
+    "@rollup/plugin-commonjs": "^11.0.1",
+    "@rollup/plugin-node-resolve": "^7.0.0",
+    "concurrently": "^3.6.1",
+    "http-server": "^0.12.1",
+    "jsdoc": "^3.6.3",
+    "markdownlint-cli": "^0.19.0",
+    "rollup": "^1.30.0",
+    "rollup-cli": "^1.0.9",
+    "standard": "^14.0.0",
+    "tui-jsdoc-template": "^1.2.2",
+    "typescript": "^3.7.5",
+    "y-protocols": "^0.2.3"
  }
 }
--- a/rollup.browser.js
+++ b/rollup.browser.js
@@ -1,47 +0,0 @@
-import inject from 'rollup-plugin-inject'
-import babel from 'rollup-plugin-babel'
-import uglify from 'rollup-plugin-uglify'
-import nodeResolve from 'rollup-plugin-node-resolve'
-import commonjs from 'rollup-plugin-commonjs'
-var pkg = require('./package.json')
-
-export default {
-  entry: 'src/y.js',
-  moduleName: 'Y',
-  format: 'umd',
-  plugins: [
-    nodeResolve({
-      main: true,
-      module: true,
-      browser: true
-    }),
-    commonjs(),
-    babel({
-      runtimeHelpers: true
-    }),
-    inject({
-      regeneratorRuntime: 'regenerator-runtime'
-    }),
-    uglify({
-      output: {
-        comments: function (node, comment) {
-          var text = comment.value
-          var type = comment.type
-          if (type === 'comment2') {
-            // multiline comment
-            return /@license/i.test(text)
-          }
-        }
-      }
-    })
-  ],
-  dest: 'y.js',
-  sourceMap: true,
-  banner: `
-/**
- * ${pkg.name} - ${pkg.description}
- * @version v${pkg.version}
- * @license ${pkg.license}
- */
-`
-}
--- a/rollup.config.js
+++ b/rollup.config.js
@@ -0,0 +1,94 @@
+import nodeResolve from '@rollup/plugin-node-resolve'
+import commonjs from '@rollup/plugin-commonjs'
+
+const localImports = process.env.LOCALIMPORTS
+
+const customModules = new Set([
+  'y-websocket',
+  'y-codemirror',
+  'y-ace',
+  'y-textarea',
+  'y-quill',
+  'y-dom',
+  'y-prosemirror'
+])
+/**
+ * @type {Set<any>}
+ */
+const customLibModules = new Set([
+  'lib0',
+  'y-protocols'
+])
+const debugResolve = {
+  resolveId (importee) {
+    if (importee === 'yjs') {
+      return `${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, -3)}.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/rollup.node.js
+++ b/rollup.node.js
@@ -1,26 +0,0 @@
-import nodeResolve from 'rollup-plugin-node-resolve'
-import commonjs from 'rollup-plugin-commonjs'
-var pkg = require('./package.json')
-
-export default {
-  entry: 'src/y.js',
-  moduleName: 'Y',
-  format: 'umd',
-  plugins: [
-    nodeResolve({
-      main: true,
-      module: true,
-      browser: true
-    }),
-    commonjs()
-  ],
-  dest: 'y.node.js',
-  sourceMap: true,
-  banner: `
-/**
- * ${pkg.name} - ${pkg.description}
- * @version v${pkg.version}
- * @license ${pkg.license}
- */
-`
-}
--- a/rollup.test.js
+++ b/rollup.test.js
@@ -1,20 +0,0 @@
-import nodeResolve from 'rollup-plugin-node-resolve'
-import commonjs from 'rollup-plugin-commonjs'
-import multiEntry from 'rollup-plugin-multi-entry'
-
-export default {
-  entry: 'tests/*.js',
-  moduleName: 'y-array-tests',
-  format: 'umd',
-  plugins: [
-    nodeResolve({
-      main: true,
-      module: true,
-      browser: true
-    }),
-    commonjs(),
-    multiEntry()
-  ],
-  dest: 'y-array.test.js',
-  sourceMap: true
-}
--- a/src/Connector.js
+++ b/src/Connector.js
@@ -1,491 +0,0 @@
-
-function canRead (auth) { return auth === 'read' || auth === 'write' }
-function canWrite (auth) { return auth === 'write' }
-
-export default function extendConnector (Y/* :any */) {
-  class AbstractConnector {
-    /* ::
-    y: YConfig;
-    role: SyncRole;
-    connections: Object;
-    isSynced: boolean;
-    userEventListeners: Array<Function>;
-    whenSyncedListeners: Array<Function>;
-    currentSyncTarget: ?UserId;
-    syncingClients: Array<UserId>;
-    forwardToSyncingClients: boolean;
-    debug: boolean;
-    syncStep2: Promise;
-    userId: UserId;
-    send: Function;
-    broadcast: Function;
-    broadcastOpBuffer: Array<Operation>;
-    protocolVersion: number;
-    */
-    /*
-      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 = {}
-      }
-      // Prefer to receive untransformed operations. This does only work if
-      // this client receives operations from only one other client.
-      // In particular, this does not work with y-webrtc.
-      // It will work with y-websockets-client
-      this.preferUntransformed = opts.preferUntransformed || false
-      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.log = Y.debug('y:connector')
-      this.logMessage = Y.debug('y:connector-message')
-      this.y.db.forwardAppliedOperations = opts.forwardAppliedOperations || false
-      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.broadcastOpBuffer = []
-      this.protocolVersion = 11
-      this.authInfo = opts.auth || null
-      this.checkAuth = opts.checkAuth || function () { return Promise.resolve('write') } // default is everyone has write access
-      if (opts.generateUserId !== false) {
-        this.setUserId(Y.utils.generateGuid())
-      }
-    }
-    resetAuth (auth) {
-      if (this.authInfo !== auth) {
-        this.authInfo = auth
-        this.broadcast({
-          type: 'auth',
-          auth: this.authInfo
-        })
-      }
-    }
-    reconnect () {
-      this.log('reconnecting..')
-      return this.y.db.startGarbageCollector()
-    }
-    disconnect () {
-      this.log('discronnecting..')
-      this.connections = {}
-      this.isSynced = false
-      this.currentSyncTarget = null
-      this.syncingClients = []
-      this.whenSyncedListeners = []
-      this.y.db.stopGarbageCollector()
-      return this.y.db.whenTransactionsFinished()
-    }
-    repair () {
-      this.log('Repairing the state of Yjs. This can happen if messages get lost, and Yjs detects that something is wrong. If this happens often, please report an issue here: https://github.com/y-js/yjs/issues')
-      for (var name in this.connections) {
-        this.connections[name].isSynced = false
-      }
-      this.isSynced = false
-      this.currentSyncTarget = null
-      this.findNextSyncTarget()
-    }
-    setUserId (userId) {
-      if (this.userId == null) {
-        this.log('Set userId to "%s"', userId)
-        this.userId = userId
-        return this.y.db.setUserId(userId)
-      } else {
-        return null
-      }
-    }
-    onUserEvent (f) {
-      this.userEventListeners.push(f)
-    }
-    removeUserEventListener (f) {
-      this.userEventListeners = this.userEventListeners.filter(g => f !== g)
-    }
-    userLeft (user) {
-      if (this.connections[user] != null) {
-        this.log('User left: %s', 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.log('User joined: %s', user)
-      this.connections[user] = {
-        isSynced: false,
-        role: role
-      }
-      let defer = {}
-      defer.promise = new Promise(function (resolve) { defer.resolve = resolve })
-      this.connections[user].syncStep2 = defer
-      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)
-      }
-    }
-    findNextSyncTarget () {
-      if (this.currentSyncTarget != null) {
-        return // "The current sync has not finished!"
-      }
-
-      var syncUser = null
-      for (var uid in this.connections) {
-        if (!this.connections[uid].isSynced) {
-          syncUser = uid
-          break
-        }
-      }
-      var conn = this
-      if (syncUser != null) {
-        this.currentSyncTarget = syncUser
-        this.y.db.requestTransaction(function * () {
-          var stateSet = yield * this.getStateSet()
-          // var deleteSet = yield * this.getDeleteSet()
-          var answer = {
-            type: 'sync step 1',
-            stateSet: stateSet,
-            // deleteSet: deleteSet,
-            protocolVersion: conn.protocolVersion,
-            auth: conn.authInfo
-          }
-          if (conn.preferUntransformed && Object.keys(stateSet).length === 0) {
-            answer.preferUntransformed = true
-          }
-          conn.send(syncUser, answer)
-        })
-      } else {
-        if (!conn.isSynced) {
-          this.y.db.requestTransaction(function * () {
-            if (!conn.isSynced) {
-              // it is crucial that isSynced is set at the time garbageCollectAfterSync is called
-              conn.isSynced = true
-              // It is safer to remove this!
-              // TODO: remove: yield * this.garbageCollectAfterSync()
-              // call whensynced listeners
-              for (var f of conn.whenSyncedListeners) {
-                f()
-              }
-              conn.whenSyncedListeners = []
-            }
-          })
-        }
-      }
-    }
-    send (uid, message) {
-      this.log('Send \'%s\' to %s', message.type, uid)
-      this.logMessage('Message: %j', message)
-    }
-    broadcast (message) {
-      this.log('Broadcast \'%s\'', message.type)
-      this.logMessage('Message: %j', message)
-    }
-    /*
-      Buffer operations, and broadcast them when ready.
-    */
-    broadcastOps (ops) {
-      ops = ops.map(function (op) {
-        return Y.Struct[op.struct].encode(op)
-      })
-      var self = this
-      function broadcastOperations () {
-        if (self.broadcastOpBuffer.length > 0) {
-          self.broadcast({
-            type: 'update',
-            ops: self.broadcastOpBuffer
-          })
-          self.broadcastOpBuffer = []
-        }
-      }
-      if (this.broadcastOpBuffer.length === 0) {
-        this.broadcastOpBuffer = ops
-        this.y.db.whenTransactionsFinished().then(broadcastOperations)
-      } else {
-        this.broadcastOpBuffer = this.broadcastOpBuffer.concat(ops)
-      }
-    }
-    /*
-      You received a raw message, and you know that it is intended for Yjs. Then call this function.
-    */
-    receiveMessage (sender/* :UserId */, message/* :Message */) {
-      if (sender === this.userId) {
-        return Promise.resolve()
-      }
-      this.log('Receive \'%s\' from %s', message.type, sender)
-      this.logMessage('Message: %j', message)
-      if (message.protocolVersion != null && message.protocolVersion !== this.protocolVersion) {
-        this.log(
-          `You tried to sync with a yjs instance that has a different protocol version
-          (You: ${this.protocolVersion}, Client: ${message.protocolVersion}).
-          The sync was stopped. You need to upgrade your dependencies (especially Yjs & the Connector)!
-          `)
-        this.send(sender, {
-          type: 'sync stop',
-          protocolVersion: this.protocolVersion
-        })
-        return Promise.reject(new Error('Incompatible protocol version'))
-      }
-      if (message.auth != null && this.connections[sender] != null) {
-        // authenticate using auth in message
-        var auth = this.checkAuth(message.auth, this.y)
-        this.connections[sender].auth = auth
-        auth.then(auth => {
-          for (var f of this.userEventListeners) {
-            f({
-              action: 'userAuthenticated',
-              user: sender,
-              auth: auth
-            })
-          }
-        })
-      } else if (this.connections[sender] != null && this.connections[sender].auth == null) {
-        // authenticate without otherwise
-        this.connections[sender].auth = this.checkAuth(null, this.y)
-      }
-      if (this.connections[sender] != null && this.connections[sender].auth != null) {
-        return this.connections[sender].auth.then((auth) => {
-          if (message.type === 'sync step 1' && canRead(auth)) {
-            let conn = this
-            let m = message
-            let wait // wait for sync step 2 to complete
-            if (this.role === 'slave') {
-              wait = Promise.all(Object.keys(this.connections)
-                .map(uid => this.connections[uid])
-                .filter(conn => conn.role === 'master')
-                .map(conn => conn.syncStep2.promise)
-              )
-            } else {
-              wait = Promise.resolve()
-            }
-            wait.then(() => {
-              this.y.db.requestTransaction(function * () {
-                var currentStateSet = yield * this.getStateSet()
-                // TODO: remove
-                // if (canWrite(auth)) {
-                //  yield * this.applyDeleteSet(m.deleteSet)
-                // }
-
-                var ds = yield * this.getDeleteSet()
-                var answer = {
-                  type: 'sync step 2',
-                  stateSet: currentStateSet,
-                  deleteSet: ds,
-                  protocolVersion: this.protocolVersion,
-                  auth: this.authInfo
-                }
-                if (message.preferUntransformed === true && Object.keys(m.stateSet).length === 0) {
-                  answer.osUntransformed = yield * this.getOperationsUntransformed()
-                } else {
-                  answer.os = yield * this.getOperations(m.stateSet)
-                }
-                conn.send(sender, answer)
-                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'
-                    })
-                  }, 5000) // TODO: conn.syncingClientDuration)
-                } else {
-                  conn.send(sender, {
-                    type: 'sync done'
-                  })
-                }
-              })
-            })
-          } else if (message.type === 'sync step 2' && canWrite(auth)) {
-            var db = this.y.db
-            let defer = this.connections[sender].syncStep2
-            let m = message
-            // apply operations first
-            db.requestTransaction(function * () {
-              // yield * this.applyDeleteSet(m.deleteSet)
-              if (m.osUntransformed != null) {
-                yield * this.applyOperationsUntransformed(m.osUntransformed, m.stateSet)
-              } else {
-                this.store.apply(m.os)
-              }
-              // defer.resolve()
-            })
-            // then apply ds
-            db.whenTransactionsFinished().then(() => {
-              db.requestTransaction(function * () {
-                yield * this.applyDeleteSet(m.deleteSet)
-              })
-              defer.resolve()
-            })
-            return defer.promise
-          } else if (message.type === 'sync done') {
-            var self = this
-            this.connections[sender].syncStep2.promise.then(function () {
-              self._setSyncedWith(sender)
-            })
-          } else if (message.type === 'update' && canWrite(auth)) {
-            if (this.forwardToSyncingClients) {
-              for (var client of this.syncingClients) {
-                this.send(client, message)
-              }
-            }
-            if (this.y.db.forwardAppliedOperations) {
-              var delops = message.ops.filter(function (o) {
-                return o.struct === 'Delete'
-              })
-              if (delops.length > 0) {
-                this.broadcastOps(delops)
-              }
-            }
-            this.y.db.apply(message.ops)
-          }
-        })
-      } else {
-        return Promise.reject(new Error('Unable to deliver message'))
-      }
-    }
-    _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/* :any */) {
-      function parseArray (node) {
-        for (var n of node.children) {
-          if (n.getAttribute('isArray') === 'true') {
-            return parseArray(n)
-          } else {
-            return parseObject(n)
-          }
-        }
-      }
-      function parseObject (node/* :any */) {
-        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/* :any */ 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
@@ -1,178 +0,0 @@
-/* global getRandom, async */
-'use strict'
-
-module.exports = function (Y) {
-  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')
-        }
-      }
-    },
-    whenTransactionsFinished: function () {
-      var self = this
-      return new Promise(function (resolve, reject) {
-        // The connector first has to send the messages to the db.
-        // Wait for the checkAuth-function to resolve
-        // The test lib only has a simple checkAuth function: `() => Promise.resolve()`
-        // Just add a function to the event-queue, in order to wait for the event.
-        // TODO: this may be buggy in test applications (but it isn't be for real-life apps)
-        setTimeout(function () {
-          var ps = []
-          for (var name in self.users) {
-            ps.push(self.users[name].y.db.whenTransactionsFinished())
-          }
-          Promise.all(ps).then(resolve, reject)
-        }, 10)
-      })
-    },
-    flushOne: function flushOne () {
-      var bufs = []
-      for (var receiver in globalRoom.buffers) {
-        let buff = globalRoom.buffers[receiver]
-        var push = false
-        for (let sender in buff) {
-          if (buff[sender].length > 0) {
-            push = true
-            break
-          }
-        }
-        if (push) {
-          bufs.push(receiver)
-        }
-      }
-      if (bufs.length > 0) {
-        var userId = getRandom(bufs)
-        let buff = globalRoom.buffers[userId]
-        let sender = getRandom(Object.keys(buff))
-        var m = buff[sender].shift()
-        if (buff[sender].length === 0) {
-          delete buff[sender]
-        }
-        var user = globalRoom.users[userId]
-        return user.receiveMessage(m[0], m[1]).then(function () {
-          return user.y.db.whenTransactionsFinished()
-        }, function () {})
-      } else {
-        return false
-      }
-    },
-    flushAll: function () {
-      return new Promise(function (resolve) {
-        // flushes may result in more created operations,
-        // flush until there is nothing more to flush
-        function nextFlush () {
-          var c = globalRoom.flushOne()
-          if (c) {
-            while (c) {
-              c = globalRoom.flushOne()
-            }
-            globalRoom.whenTransactionsFinished().then(nextFlush)
-          } else {
-            c = globalRoom.flushOne()
-            if (c) {
-              c.then(function () {
-                globalRoom.whenTransactionsFinished().then(nextFlush)
-              })
-            } else {
-              resolve()
-            }
-          }
-        }
-        globalRoom.whenTransactionsFinished().then(nextFlush)
-      })
-    }
-  }
-  Y.utils.globalRoom = globalRoom
-
-  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) {
-      return super.receiveMessage(sender, JSON.parse(JSON.stringify(m)))
-    }
-    send (userId, message) {
-      var buffer = globalRoom.buffers[userId]
-      if (buffer != null) {
-        if (buffer[this.userId] == null) {
-          buffer[this.userId] = []
-        }
-        buffer[this.userId].push(JSON.parse(JSON.stringify([this.userId, message])))
-      }
-    }
-    broadcast (message) {
-      for (var key in globalRoom.buffers) {
-        var buff = globalRoom.buffers[key]
-        if (buff[this.userId] == null) {
-          buff[this.userId] = []
-        }
-        buff[this.userId].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 Y.utils.globalRoom.flushAll()
-    }
-    disconnect () {
-      var waitForMe = Promise.resolve()
-      if (!this.isDisconnected()) {
-        globalRoom.removeUser(this.userId)
-        waitForMe = super.disconnect()
-      }
-      var self = this
-      return waitForMe.then(function () {
-        return self.y.db.whenTransactionsFinished()
-      })
-    }
-    flush () {
-      var self = this
-      return async(function * () {
-        var buff = globalRoom.buffers[self.userId]
-        while (Object.keys(buff).length > 0) {
-          var sender = getRandom(Object.keys(buff))
-          var m = buff[sender].shift()
-          if (buff[sender].length === 0) {
-            delete buff[sender]
-          }
-          yield this.receiveMessage(m[0], m[1])
-        }
-        yield self.whenTransactionsFinished()
-      })
-    }
-  }
-
-  Y.Test = Test
-}
--- a/src/Database.js
+++ b/src/Database.js
@@ -1,605 +0,0 @@
-/* @flow */
-'use strict'
-
-export default function extendDatabase (Y /* :any */) {
-  /*
-    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 {
-    /* ::
-    y: YConfig;
-    forwardAppliedOperations: boolean;
-    listenersById: Object;
-    listenersByIdExecuteNow: Array<Object>;
-    listenersByIdRequestPending: boolean;
-    initializedTypes: Object;
-    whenUserIdSetListener: ?Function;
-    waitingTransactions: Array<Transaction>;
-    transactionInProgress: boolean;
-    executeOrder: Array<Object>;
-    gc1: Array<Struct>;
-    gc2: Array<Struct>;
-    gcTimeout: number;
-    gcInterval: any;
-    garbageCollect: Function;
-    executeOrder: Array<any>; // for debugging only
-    userId: UserId;
-    opClock: number;
-    transactionsFinished: ?{promise: Promise, resolve: any};
-    transact: (x: ?Generator) => any;
-    */
-    constructor (y, opts) {
-      this.y = y
-      opts.gc = opts.gc === true
-      this.dbOpts = opts
-      var os = this
-      this.userId = null
-      var resolve_
-      this.userIdPromise = new Promise(function (resolve) {
-        resolve_ = resolve
-      })
-      this.userIdPromise.resolve = resolve_
-      // whether to broadcast all applied operations (insert & delete hook)
-      this.forwardAppliedOperations = false
-      // 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.waitingTransactions = []
-      this.transactionInProgress = false
-      this.transactionIsFlushed = false
-      if (typeof YConcurrencyTestingMode !== 'undefined') {
-        this.executeOrder = []
-      }
-      this.gc1 = [] // first stage
-      this.gc2 = [] // second stage -> after that, remove the op
-
-      function garbageCollect () {
-        return os.whenTransactionsFinished().then(function () {
-          if (os.gcTimeout > 0 && (os.gc1.length > 0 || os.gc2.length > 0)) {
-            if (!os.y.connector.isSynced) {
-              console.warn('gc should be empty when not synced!')
-            }
-            return new Promise((resolve) => {
-              os.requestTransaction(function * () {
-                if (os.y.connector != null && os.y.connector.isSynced) {
-                  for (var i = 0; i < os.gc2.length; i++) {
-                    var oid = os.gc2[i]
-                    yield * this.garbageCollectOperation(oid)
-                  }
-                  os.gc2 = os.gc1
-                  os.gc1 = []
-                }
-                // TODO: Use setInterval here instead (when garbageCollect is called several times there will be several timeouts..)
-                if (os.gcTimeout > 0) {
-                  os.gcInterval = setTimeout(garbageCollect, os.gcTimeout)
-                }
-                resolve()
-              })
-            })
-          } else {
-            // TODO: see above
-            if (os.gcTimeout > 0) {
-              os.gcInterval = setTimeout(garbageCollect, os.gcTimeout)
-            }
-            return Promise.resolve()
-          }
-        })
-      }
-      this.garbageCollect = garbageCollect
-      this.startGarbageCollector()
-
-      this.repairCheckInterval = !opts.repairCheckInterval ? 6000 : opts.repairCheckInterval
-      this.opsReceivedTimestamp = new Date()
-      this.startRepairCheck()
-    }
-    startGarbageCollector () {
-      this.gc = this.dbOpts.gc
-      if (this.gc) {
-        this.gcTimeout = !this.dbOpts.gcTimeout ? 100000 : this.dbOpts.gcTimeout
-      } else {
-        this.gcTimeout = -1
-      }
-      if (this.gcTimeout > 0) {
-        this.garbageCollect()
-      }
-    }
-    startRepairCheck () {
-      var os = this
-      if (this.repairCheckInterval > 0) {
-        this.repairCheckIntervalHandler = setInterval(function repairOnMissingOperations () {
-          /*
-            Case 1. No ops have been received in a while (new Date() - os.opsReceivedTimestamp > os.repairCheckInterval)
-              - 1.1 os.listenersById is empty. Then the state was correct the whole time. -> Nothing to do (nor to update)
-              - 1.2 os.listenersById is not empty.
-                      * Then the state was incorrect for at least {os.repairCheckInterval} seconds.
-                      * -> Remove everything in os.listenersById and sync again (connector.repair())
-            Case 2. An op has been received in the last {os.repairCheckInterval } seconds.
-                    It is not yet necessary to check for faulty behavior. Everything can still resolve itself. Wait for more messages.
-                    If nothing was received for a while and os.listenersById is still not emty, we are in case 1.2
-                    -> Do nothing
-
-            Baseline here is: we really only have to catch case 1.2..
-          */
-          if (
-            new Date() - os.opsReceivedTimestamp > os.repairCheckInterval &&
-            Object.keys(os.listenersById).length > 0 // os.listenersById is not empty
-          ) {
-            // haven't received operations for over {os.repairCheckInterval} seconds, resend state vector
-            os.listenersById = {}
-            os.opsReceivedTimestamp = new Date() // update so you don't send repair several times in a row
-            os.y.connector.repair()
-          }
-        }, this.repairCheckInterval)
-      }
-    }
-    stopRepairCheck () {
-      clearInterval(this.repairCheckIntervalHandler)
-    }
-    queueGarbageCollector (id) {
-      if (this.y.connector.isSynced && this.gc) {
-        this.gc1.push(id)
-      }
-    }
-    emptyGarbageCollector () {
-      return new Promise(resolve => {
-        var check = () => {
-          if (this.gc1.length > 0 || this.gc2.length > 0) {
-            this.garbageCollect().then(check)
-          } else {
-            resolve()
-          }
-        }
-        setTimeout(check, 0)
-      })
-    }
-    addToDebug () {
-      if (typeof YConcurrencyTestingMode !== 'undefined') {
-        var command /* :string */ = 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
-      this.gc = false
-      this.gcTimeout = -1
-      return new Promise(function (resolve) {
-        self.requestTransaction(function * () {
-          var ungc /* :Array<Struct> */ = self.gc1.concat(self.gc2)
-          self.gc1 = []
-          self.gc2 = []
-          for (var i = 0; i < ungc.length; i++) {
-            var op = yield * this.getOperation(ungc[i])
-            if (op != null) {
-              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 & gc turned on
-      * 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.store.gc &&
-        this.store.y.connector.isSynced
-      ) {
-        var gc = false
-        if (left != null && left.deleted === true) {
-          gc = true
-        } else if (op.content != null && op.content.length > 1) {
-          op = yield * this.getInsertionCleanStart([op.id[0], op.id[1] + 1])
-          gc = true
-        }
-        if (gc) {
-          op.gc = true
-          yield * this.setOperation(op)
-          this.store.queueGarbageCollector(op.id)
-          return true
-        }
-      }
-      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
-    }
-    destroyTypes () {
-      for (var key in this.initializedTypes) {
-        var type = this.initializedTypes[key]
-        if (type._destroy != null) {
-          type._destroy()
-        } else {
-          console.error('The type you included does not provide destroy functionality, it will remain in memory (updating your packages will help).')
-        }
-      }
-    }
-    * destroy () {
-      clearTimeout(this.gcInterval)
-      this.gcInterval = null
-      this.stopRepairCheck()
-    }
-    setUserId (userId) {
-      if (!this.userIdPromise.inProgress) {
-        this.userIdPromise.inProgress = true
-        var self = this
-        self.requestTransaction(function * () {
-          self.userId = userId
-          var state = yield * this.getState(userId)
-          self.opClock = state.clock
-          self.userIdPromise.resolve(userId)
-        })
-      }
-      return this.userIdPromise
-    }
-    whenUserIdSet (f) {
-      this.userIdPromise.then(f)
-    }
-    getNextOpId (numberOfIds) {
-      if (numberOfIds == null) {
-        throw new Error('getNextOpId expects the number of created ids to create!')
-      } else if (this.userId == null) {
-        throw new Error('OperationStore not yet initialized!')
-      } else {
-        var id = [this.userId, this.opClock]
-        this.opClock += numberOfIds
-        return id
-      }
-    }
-    /*
-      Apply a list of operations.
-
-      * we save a timestamp, because we received new operations that could resolve ops in this.listenersById (see this.startRepairCheck)
-      * 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) {
-      this.opsReceivedTimestamp = new Date()
-      for (var i = 0; i < ops.length; i++) {
-        var o = ops[i]
-        if (o.id == null || o.id[0] !== this.y.connector.userId) {
-          var required = Y.Struct[o.struct].requiredOps(o)
-          if (o.requires != null) {
-            required = required.concat(o.requires)
-          }
-          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 i = 0; i < ids.length; i++) {
-          let id = ids[i]
-          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 = 0; key < exeNow.length; key++) {
-          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)
-          var op
-          if (typeof id[1] === 'string') {
-            op = yield * this.getOperation(id)
-          } else {
-            op = yield * this.getInsertion(id)
-          }
-          if (op == null) {
-            store.listenersById[sid] = l
-          } else {
-            for (let i = 0; i < l.length; i++) {
-              let listener = l[i]
-              let o = listener.op
-              if (--listener.missing === 0) {
-                yield * store.tryExecute.call(this, o)
-              }
-            }
-          }
-        }
-      })
-    }
-    /*
-      Actually execute an operation, when all expected operations are available.
-    */
-    /* :: // TODO: this belongs somehow to transaction
-    store: Object;
-    getOperation: any;
-    isGarbageCollected: any;
-    addOperation: any;
-    whenOperationsExist: any;
-    */
-    * 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)
-        // this is now called in Transaction.deleteOperation!
-        // yield * this.store.operationAdded(this, op)
-      } else {
-        // check if this op was defined
-        var defined = yield * this.getInsertion(op.id)
-        while (defined != null && defined.content != null) {
-          // check if this op has a longer content in the case it is defined
-          if (defined.id[1] + defined.content.length < op.id[1] + op.content.length) {
-            var overlapSize = defined.content.length - (op.id[1] - defined.id[1])
-            op.content.splice(0, overlapSize)
-            op.id = [op.id[0], op.id[1] + overlapSize]
-            op.left = Y.utils.getLastId(defined)
-            op.origin = op.left
-            defined = yield * this.getOperation(op.id) // getOperation suffices here
-          } else {
-            break
-          }
-        }
-        if (defined == null) {
-          var opid = op.id
-          var isGarbageCollected = yield * this.isGarbageCollected(opid)
-          if (!isGarbageCollected) {
-            // TODO: reduce number of get / put calls for op ..
-            yield * Y.Struct[op.struct].execute.call(this, op)
-            yield * this.addOperation(op)
-            yield * this.store.operationAdded(this, op)
-            // operationAdded can change op..
-            op = yield * this.getOperation(opid)
-            // if insertion, try to combine with left
-            yield * this.tryCombineWithLeft(op)
-          }
-        }
-      }
-    }
-    /*
-     * Called by a transaction when an operation is added.
-     * This function is especially important for y-indexeddb, where several instances may share a single database.
-     * Every time an operation is created by one instance, it is send to all other instances and operationAdded is called
-     *
-     * If it's not a Delete operation:
-     *   * Checks if another operation is executable (listenersById)
-     *   * Update state, if possible
-     *
-     * Always:
-     *   * Call type
-     */
-    * operationAdded (transaction, op) {
-      if (op.struct === 'Delete') {
-        var type = this.initializedTypes[JSON.stringify(op.targetParent)]
-        if (type != null) {
-          yield * type._changed(transaction, op)
-        }
-      } else {
-        // increase SS
-        yield * transaction.updateState(op.id[0])
-        var opLen = op.content != null ? op.content.length : 1
-        for (let i = 0; i < opLen; i++) {
-          // notify whenOperation listeners (by id)
-          var sid = JSON.stringify([op.id[0], op.id[1] + i])
-          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)]
-
-        // if parent is deleted, mark as gc'd and return
-        if (op.parent != null) {
-          var parentIsDeleted = yield * transaction.isDeleted(op.parent)
-          if (parentIsDeleted) {
-            yield * transaction.deleteList(op.id)
-            return
-          }
-        }
-
-        // notify parent, if it was instanciated as a custom type
-        if (t != null) {
-          let o = Y.utils.copyOperation(op)
-          yield * t._changed(transaction, o)
-        }
-        if (!op.deleted) {
-          // Delete if DS says this is actually deleted
-          var len = op.content != null ? op.content.length : 1
-          var startId = op.id // You must not use op.id in the following loop, because op will change when deleted
-            // TODO: !! console.log('TODO: change this before commiting')
-          for (let i = 0; i < len; i++) {
-            var id = [startId[0], startId[1] + i]
-            var opIsDeleted = yield * transaction.isDeleted(id)
-            if (opIsDeleted) {
-              var delop = {
-                struct: 'Delete',
-                target: id
-              }
-              yield * this.tryExecute.call(transaction, delop)
-            }
-          }
-        }
-      }
-    }
-    whenTransactionsFinished () {
-      if (this.transactionInProgress) {
-        if (this.transactionsFinished == null) {
-          var resolve_
-          var promise = new Promise(function (resolve) {
-            resolve_ = resolve
-          })
-          this.transactionsFinished = {
-            resolve: resolve_,
-            promise: promise
-          }
-        }
-        return this.transactionsFinished.promise
-      } else {
-        return Promise.resolve()
-      }
-    }
-    // Check if there is another transaction request.
-    // * the last transaction is always a flush :)
-    getNextRequest () {
-      if (this.waitingTransactions.length === 0) {
-        if (this.transactionIsFlushed) {
-          this.transactionInProgress = false
-          this.transactionIsFlushed = false
-          if (this.transactionsFinished != null) {
-            this.transactionsFinished.resolve()
-            this.transactionsFinished = null
-          }
-          return null
-        } else {
-          this.transactionIsFlushed = true
-          return function * () {
-            yield * this.flush()
-          }
-        }
-      } else {
-        this.transactionIsFlushed = false
-        return this.waitingTransactions.shift()
-      }
-    }
-    requestTransaction (makeGen/* :any */, callImmediately) {
-      this.waitingTransactions.push(makeGen)
-      if (!this.transactionInProgress) {
-        this.transactionInProgress = true
-        setTimeout(() => {
-          this.transact(this.getNextRequest())
-        }, 0)
-      }
-    }
-    /*
-      Get a created/initialized type.
-    */
-    getType (id) {
-      return this.initializedTypes[JSON.stringify(id)]
-    }
-    /*
-      Init type. This is called when a remote operation is retrieved, and transformed to a type
-      TODO: delete type from store.initializedTypes[id] when corresponding id was deleted!
-    */
-    * initType (id, args) {
-      var sid = JSON.stringify(id)
-      var t = this.store.initializedTypes[sid]
-      if (t == null) {
-        var op/* :MapStruct | ListStruct */ = yield * this.getOperation(id)
-        if (op != null) {
-          t = yield * Y[op.type].typeDefinition.initType.call(this, this.store, op, args)
-          this.store.initializedTypes[sid] = t
-        }
-      }
-      return t
-    }
-    /*
-     Create type. This is called when the local user creates a type (which is a synchronous action)
-    */
-    createType (typedefinition, id) {
-      var structname = typedefinition[0].struct
-      id = id || this.getNextOpId(1)
-      var op = Y.Struct[structname].create(id)
-      op.type = typedefinition[0].name
-
-      this.requestTransaction(function * () {
-        if (op.id[0] === '_') {
-          yield * this.setOperation(op)
-        } else {
-          yield * this.applyCreatedOperations([op])
-        }
-      })
-      var t = Y[op.type].typeDefinition.createType(this, op, typedefinition[1])
-      this.initializedTypes[JSON.stringify(op.id)] = t
-      return t
-    }
-  }
-  Y.AbstractDatabase = AbstractDatabase
-}
--- a/src/Database.spec.js
+++ b/src/Database.spec.js
@@ -1,354 +0,0 @@
-/* global async, databases, describe, beforeEach, afterEach */
-/* eslint-env browser,jasmine,console */
-'use strict'
-
-var Y = require('./SpecHelper.js')
-
-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], 1)
-            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], 1)
-            yield * this.markDeleted(['u1', 11], 1)
-            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], 1)
-            yield * this.markDeleted(['0', 4], 1)
-            yield * this.markDeleted(['0', 2], 1)
-            expect(yield * this.getDeleteSet()).toEqual({'0': [[2, 3, false]]})
-            done()
-          })
-        }))
-        it('Debug #1', async(function * (done) {
-          store.requestTransaction(function * () {
-            yield * this.markDeleted(['166', 0], 1)
-            yield * this.markDeleted(['166', 2], 1)
-            yield * this.markDeleted(['166', 0], 1)
-            yield * this.markDeleted(['166', 2], 1)
-            yield * this.markGarbageCollected(['166', 2], 1)
-            yield * this.markDeleted(['166', 1], 1)
-            yield * this.markDeleted(['166', 3], 1)
-            yield * this.markGarbageCollected(['166', 3], 1)
-            yield * this.markDeleted(['166', 0], 1)
-            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], 1)
-            yield * this.markDeleted(['291', 2], 1)
-            yield * this.markDeleted(['291', 2], 1)
-            yield * this.markGarbageCollected(['293', 0], 1)
-            yield * this.markDeleted(['293', 1], 1)
-            yield * this.markGarbageCollected(['291', 2], 1)
-            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], 1)
-            yield * this.markDeleted(['581', 1], 1)
-            yield * this.markDeleted(['580', 0], 1)
-            yield * this.markDeleted(['580', 0], 1)
-            yield * this.markGarbageCollected(['581', 0], 1)
-            yield * this.markDeleted(['581', 2], 1)
-            yield * this.markDeleted(['580', 1], 1)
-            yield * this.markDeleted(['580', 2], 1)
-            yield * this.markDeleted(['580', 1], 1)
-            yield * this.markDeleted(['580', 2], 1)
-            yield * this.markGarbageCollected(['581', 2], 1)
-            yield * this.markGarbageCollected(['581', 1], 1)
-            yield * this.markGarbageCollected(['580', 1], 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], 1)
-            yield * this.markDeleted(['543', 2], 1)
-            yield * this.markDeleted(['544', 0], 1)
-            yield * this.markDeleted(['543', 2], 1)
-            yield * this.markGarbageCollected(['544', 0], 1)
-            yield * this.markDeleted(['545', 1], 1)
-            yield * this.markDeleted(['543', 4], 1)
-            yield * this.markDeleted(['543', 3], 1)
-            yield * this.markDeleted(['544', 1], 1)
-            yield * this.markDeleted(['544', 2], 1)
-            yield * this.markDeleted(['544', 1], 1)
-            yield * this.markDeleted(['544', 2], 1)
-            yield * this.markGarbageCollected(['543', 2], 1)
-            yield * this.markGarbageCollected(['543', 4], 1)
-            yield * this.markGarbageCollected(['544', 2], 1)
-            yield * this.markGarbageCollected(['543', 3], 1)
-            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], 1)
-            yield * this.markDeleted(['11', 2], 1)
-            yield * this.markDeleted(['11', 4], 1)
-            yield * this.markDeleted(['11', 1], 1)
-            yield * this.markDeleted(['9', 4], 1)
-            yield * this.markDeleted(['10', 0], 1)
-            yield * this.markGarbageCollected(['11', 2], 1)
-            yield * this.markDeleted(['11', 2], 1)
-            yield * this.markGarbageCollected(['11', 3], 1)
-            yield * this.markDeleted(['11', 3], 1)
-            yield * this.markDeleted(['11', 3], 1)
-            yield * this.markDeleted(['9', 4], 1)
-            yield * this.markDeleted(['10', 0], 1)
-            yield * this.markGarbageCollected(['11', 1], 1)
-            yield * this.markDeleted(['11', 1], 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/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/SpecHelper.js
+++ b/src/SpecHelper.js
@@ -1,404 +0,0 @@
-/* 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 Y = require('./y.js')
-require('../../y-memory/src/Memory.js')(Y)
-require('../../y-array/src/Array.js')(Y)
-require('../../y-map/src/Map.js')(Y)
-require('../../y-indexeddb/src/IndexedDB.js')(Y)
-
-module.exports = Y
-
-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
-
-// Helper methods for the random number generator
-Math.seedrandom = require('seedrandom')
-
-g.generateRandomSeed = function generateRandomSeed () {
-  var seed
-  if (typeof window !== 'undefined' && window.location.hash.length > 1) {
-    seed = window.location.hash.slice(1) // first character is the hash!
-    console.warn('Using random seed that was specified in the url!')
-  } else {
-    seed = JSON.stringify(Math.random())
-  }
-  console.info('Using random seed: ' + seed)
-  g.setRandomSeed(seed)
-}
-
-g.setRandomSeed = function setRandomSeed (seed) {
-  Math.seedrandom.currentSeed = seed
-  Math.seedrandom(Math.seedrandom.currentSeed, { global: true })
-}
-
-g.generateRandomSeed()
-
-g.YConcurrencyTestingMode = true
-
-jasmine.DEFAULT_TIMEOUT_INTERVAL = 200000
-
-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 = 0
-  }
-  return new Promise(function (resolve) {
-    setTimeout(function () {
-      resolve()
-    }, t)
-  })
-}
-g.wait = wait
-
-g.databases = ['memory']
-if (typeof window !== 'undefined') {
-  g.databases.push('indexeddb')
-} else {
-  g.databases.push('leveldb')
-}
-/*
-  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) {
-    return o[getRandom(Object.keys(o))]
-  }
-}
-g.getRandom = getRandom
-
-function getRandomNumber (n) {
-  if (n == null) {
-    n = 9999
-  }
-  return Math.floor(Math.random() * n)
-}
-g.getRandomNumber = getRandomNumber
-
-function getRandomString () {
-  var chars = 'abcdefghijklmnopqrstuvwxyzäüöABCDEFGHIJKLMNOPQRSTUVWXYZÄÜÖ'
-  var char = chars[getRandomNumber(chars.length)] // ü\n\n\n\n\n\n\n'
-  var length = getRandomNumber(7)
-  var string = ''
-  for (var i = 0; i < length; i++) {
-    string += char
-  }
-  return string
-}
-g.getRandomString = getRandomString
-
-function * applyTransactions (relAmount, numberOfTransactions, objects, users, transactions, noReconnect) {
-  g.generateRandomSeed() // create a new seed, so we can re-create the behavior
-  for (var i = 0; i < numberOfTransactions * relAmount + 1; i++) {
-    var r = Math.random()
-    if (r > 0.95) {
-      // 10% chance of toggling concurrent user interactions.
-      // There will be an artificial delay until ops can be executed by the type,
-      // therefore, operations of the database will be (pre)transformed until user operations arrive
-      yield (function simulateConcurrentUserInteractions (type) {
-        if (!(type instanceof Y.utils.CustomType) && type.y instanceof Y.utils.CustomType) {
-          // usually we expect type to be a custom type. But in YXml we share an object {y: YXml, dom: Dom} instead
-          type = type.y
-        }
-        if (type.eventHandler.awaiting === 0 && type.eventHandler._debuggingAwaiting !== true) {
-          type.eventHandler.awaiting = 1
-          type.eventHandler._debuggingAwaiting = true
-        } else {
-          // fixAwaitingInType will handle _debuggingAwaiting
-          return fixAwaitingInType(type)
-        }
-      })(getRandom(objects))
-    } else if (r >= 0.5) {
-      // 40% chance to flush
-      yield Y.utils.globalRoom.flushOne() // flushes for some user.. (not necessarily 0)
-    } else if (noReconnect || r >= 0.05) {
-      // 45% chance to create operation
-      var done = getRandom(transactions)(getRandom(objects))
-      if (done != null) {
-        yield done
-      } else {
-        yield wait()
-      }
-      yield Y.utils.globalRoom.whenTransactionsFinished()
-    } else {
-      // 5% chance to disconnect/reconnect
-      var u = getRandom(users)
-      yield Promise.all(objects.map(fixAwaitingInType))
-      if (u.connector.isDisconnected()) {
-        yield u.reconnect()
-      } else {
-        yield u.disconnect()
-      }
-      yield Promise.all(objects.map(fixAwaitingInType))
-    }
-  }
-}
-
-function fixAwaitingInType (type) {
-  if (!(type instanceof Y.utils.CustomType) && type.y instanceof Y.utils.CustomType) {
-    // usually we expect type to be a custom type. But in YXml we share an object {y: YXml, dom: Dom} instead
-    type = type.y
-  }
-  return new Promise(function (resolve) {
-    type.os.whenTransactionsFinished().then(function () {
-      // _debuggingAwaiting artificially increases the awaiting property. We need to make sure that we only do that once / reverse the effect once
-      type.os.requestTransaction(function * () {
-        if (type.eventHandler.awaiting > 0 && type.eventHandler._debuggingAwaiting === true) {
-          type.eventHandler._debuggingAwaiting = false
-          yield * type.eventHandler.awaitOps(this, function * () { /* mock function */ })
-        }
-        wait(50).then(type.os.whenTransactionsFinished()).then(wait(50)).then(resolve)
-      })
-    })
-  })
-}
-g.fixAwaitingInType = fixAwaitingInType
-
-g.applyRandomTransactionsNoGCNoDisconnect = async(function * applyRandomTransactions (users, objects, transactions, numberOfTransactions) {
-  yield * applyTransactions(1, numberOfTransactions, objects, users, transactions, true)
-  yield Y.utils.globalRoom.flushAll()
-  yield Promise.all(objects.map(fixAwaitingInType))
-})
-
-g.applyRandomTransactionsAllRejoinNoGC = async(function * applyRandomTransactions (users, objects, transactions, numberOfTransactions) {
-  yield * applyTransactions(1, numberOfTransactions, objects, users, transactions)
-  yield Promise.all(objects.map(fixAwaitingInType))
-  yield Y.utils.globalRoom.flushAll()
-  yield Promise.all(objects.map(fixAwaitingInType))
-  for (var u in users) {
-    yield Promise.all(objects.map(fixAwaitingInType))
-    yield users[u].reconnect()
-    yield Promise.all(objects.map(fixAwaitingInType))
-  }
-  yield Promise.all(objects.map(fixAwaitingInType))
-  yield Y.utils.globalRoom.flushAll()
-  yield Promise.all(objects.map(fixAwaitingInType))
-  yield g.garbageCollectAllUsers(users)
-})
-
-g.applyRandomTransactionsWithGC = async(function * applyRandomTransactions (users, objects, transactions, numberOfTransactions) {
-  yield * applyTransactions(1, numberOfTransactions, objects, users.slice(1), transactions)
-  yield Y.utils.globalRoom.flushAll()
-  yield Promise.all(objects.map(fixAwaitingInType))
-  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 Y.utils.globalRoom.flushAll()
-  yield Promise.all(objects.map(fixAwaitingInType))
-  yield g.garbageCollectAllUsers(users)
-})
-
-g.garbageCollectAllUsers = async(function * garbageCollectAllUsers (users) {
-  yield Y.utils.globalRoom.flushAll()
-  for (var i in users) {
-    yield users[i].db.emptyGarbageCollector()
-  }
-})
-
-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
-
-  yield Y.utils.globalRoom.flushAll()
-  yield g.garbageCollectAllUsers(users)
-  yield Y.utils.globalRoom.flushAll()
-
-  // disconnect, then reconnect all users
-  // We do this to make sure that the gc is updated by everyone
-  for (var i = 0; i < users.length; i++) {
-    yield users[i].disconnect()
-    yield wait()
-    yield users[i].reconnect()
-  }
-  yield wait()
-  yield Y.utils.globalRoom.flushAll()
-
-  // 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)
-    })
-  }
-
-  var buffer = Y.utils.globalRoom.buffers
-  for (var name in buffer) {
-    if (buffer[name].length > 0) {
-      // not all ops were transmitted..
-      debugger // eslint-disable-line
-    }
-  }
-
-  for (var uid = 0; uid < users.length; uid++) {
-    var u = users[uid]
-    u.db.requestTransaction(function * () {
-      var sv = yield * this.getStateVector()
-      for (var s of sv) {
-        yield * this.updateState(s.user)
-      }
-      // 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.getInsertion([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
-    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
-          delete o.originOf
-          db1.push(o)
-        })
-      })
-    } else {
-      u.db.requestTransaction(function * () {
-        yield * t2.call(this)
-        var db2 = []
-        yield * this.os.iterate(this, null, null, function * (o) {
-          o = Y.utils.copyObject(o)
-          delete o.origin
-          delete o.originOf
-          db2.push(o)
-        })
-        expect(s1).toEqual(s2)
-        expect(allDels1).toEqual(allDels2) // inner structure
-        expect(ds1).toEqual(ds2) // exported structure
-        db2.forEach((o, i) => {
-          expect(db1[i]).toEqual(o)
-        })
-      })
-    }
-    yield u.db.whenTransactionsFinished()
-  }
-})
-
-g.createUsers = async(function * createUsers (self, numberOfUsers, database, initType) {
-  if (Y.utils.globalRoom.users[0] != null) {
-    yield Y.utils.globalRoom.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,
-        gc: true,
-        repairCheckInterval: -1
-      },
-      connector: {
-        name: 'Test',
-        debug: false
-      },
-      share: {
-        root: initType || 'Map'
-      }
-    }))
-  }
-  self.users = yield Promise.all(promises)
-  self.types = self.users.map(function (u) { return u.share.root })
-  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/Struct.js
+++ b/src/Struct.js
@@ -1,414 +0,0 @@
-/* @flow */
-'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.
-*/
-export default function extendStruct (Y) {
-  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 {
-          target: op.target,
-          length: op.length || 0,
-          struct: 'Delete'
-        }
-      },
-      requiredOps: function (op) {
-        return [] // [op.target]
-      },
-      execute: function * (op) {
-        return yield * this.deleteOperation(op.target, op.length || 1)
-      }
-    },
-    Insert: {
-      /* {
-          content: [any],
-          opContent: Id,
-          id: Id,
-          left: Id,
-          origin: Id,
-          right: Id,
-          parent: Id,
-          parentSub: string (optional), // child of Map type
-        }
-      */
-      encode: function (op/* :Insertion */) /* :Insertion */ {
-        // TODO: you could not send the "left" property, then you also have to
-        // "op.left = null" in $execute or $decode
-        var e/* :any */ = {
-          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.hasOwnProperty('opContent')) {
-          e.opContent = op.opContent
-        } else {
-          e.content = op.content.slice()
-        }
-
-        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.getInsertion(op.left)
-          while (!Y.utils.matchesId(o, op.origin)) {
-            d++
-            if (o.left == null) {
-              break
-            } else {
-              o = yield * this.getInsertion(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
-
-        // during this function some ops may get split into two pieces (e.g. with getInsertionCleanEnd)
-        // We try to merge them later, if possible
-        var tryToRemergeLater = []
-
-        if (op.origin != null) { // TODO: !== instead of !=
-          // we save in origin that op originates in it
-          // we need that later when we eventually garbage collect origin (see transaction)
-          var origin = yield * this.getInsertionCleanEnd(op.origin)
-          if (origin.originOf == null) {
-            origin.originOf = []
-          }
-          origin.originOf.push(op.id)
-          yield * this.setOperation(origin)
-          if (origin.right != null) {
-            tryToRemergeLater.push(origin.right)
-          }
-        }
-        var distanceToOrigin = i = yield * Struct.Insert.getDistanceToOrigin.call(this, op) // most cases: 0 (starts from 0)
-
-        // now we begin to insert op in the list of insertions..
-        var o
-        var parent
-        var start
-
-        // find o. o is the first conflicting operation
-        if (op.left != null) {
-          o = yield * this.getInsertionCleanEnd(op.left)
-          if (!Y.utils.compareIds(op.left, op.origin) && o.right != null) {
-            // only if not added previously
-            tryToRemergeLater.push(o.right)
-          }
-          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
-        }
-
-        // make sure to split op.right if necessary (also add to tryCombineWithLeft)
-        if (op.right != null) {
-          tryToRemergeLater.push(op.right)
-          yield * this.getInsertionCleanStart(op.right)
-        }
-
-        // 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 = Y.utils.getLastId(o)
-                distanceToOrigin = i + 1 // just ignore o.content.length, doesn't make a difference
-              }
-            } else if (oOriginDistance < i) {
-              // case 2
-              if (i - distanceToOrigin <= oOriginDistance) {
-                op.left = Y.utils.getLastId(o)
-                distanceToOrigin = i + 1 // just ignore o.content.length, doesn't make a difference
-              }
-            } else {
-              break
-            }
-            i++
-            if (o.right != null) {
-              o = yield * this.getInsertion(o.right)
-            } else {
-              o = null
-            }
-          } else {
-            break
-          }
-        }
-
-        // reconnect..
-        var left = null
-        var right = null
-        if (parent == null) {
-          parent = yield * this.getOperation(op.parent)
-        }
-
-        // reconnect left and set right of op
-        if (op.left != null) {
-          left = yield * this.getInsertion(op.left)
-          // link left
-          op.right = left.right
-          left.right = op.id
-
-          yield * this.setOperation(left)
-        } else {
-          // set op.right from parent, if necessary
-          op.right = op.parentSub ? parent.map[op.parentSub] || null : parent.start
-        }
-        // reconnect right
-        if (op.right != null) {
-          // TODO: wanna connect right too?
-          right = yield * this.getOperation(op.right)
-          right.left = Y.utils.getLastId(op)
-
-          // if right exists, and it is supposed to be gc'd. Remove it from the gc
-          if (right.gc != null) {
-            if (right.content != null && right.content.length > 1) {
-              right = yield * this.getInsertionCleanEnd(right.id)
-            }
-            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
-          // We do not call the type in this case (this is what the third parameter is for)
-          if (op.right != null) {
-            yield * this.deleteOperation(op.right, 1, true)
-          }
-          if (op.left != null) {
-            yield * this.deleteOperation(op.id, 1, true)
-          }
-        } else {
-          if (right == null || left == null) {
-            if (right == null) {
-              parent.end = Y.utils.getLastId(op)
-            }
-            if (left == null) {
-              parent.start = op.id
-            }
-            yield * this.setOperation(parent)
-          }
-        }
-
-        // try to merge original op.left and op.origin
-        for (i = 0; i < tryToRemergeLater.length; i++) {
-          var m = yield * this.getOperation(tryToRemergeLater[i])
-          yield * this.tryCombineWithLeft(m)
-        }
-      }
-    },
-    List: {
-      /*
-      {
-        start: null,
-        end: null,
-        struct: "List",
-        type: "",
-        id: this.os.getNextOpId(1)
-      }
-      */
-      create: function (id) {
-        return {
-          start: null,
-          end: null,
-          struct: 'List',
-          id: id
-        }
-      },
-      encode: function (op) {
-        var e = {
-          struct: 'List',
-          id: op.id,
-          type: op.type
-        }
-        if (op.requires != null) {
-          e.requires = op.requires
-        }
-        if (op.info != null) {
-          e.info = op.info
-        }
-        return e
-      },
-      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(1)
-        }
-      */
-      create: function (id) {
-        return {
-          id: id,
-          map: {},
-          struct: 'Map'
-        }
-      },
-      encode: function (op) {
-        var e = {
-          struct: 'Map',
-          type: op.type,
-          id: op.id,
-          map: {} // overwrite map!!
-        }
-        if (op.requires != null) {
-          e.requires = op.requires
-        }
-        if (op.info != null) {
-          e.info = op.info
-        }
-        return e
-      },
-      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)
-          if (res == null || res.deleted) {
-            return void 0
-          } else if (res.opContent == null) {
-            return res.content[0]
-          } else {
-            return yield * this.getType(res.opContent)
-          }
-        }
-      }
-    }
-  }
-  Y.Struct = Struct
-}
--- a/src/Transaction.js
+++ b/src/Transaction.js
--- a/src/Utils.js
+++ b/src/Utils.js
@@ -1,825 +0,0 @@
-/*
-  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"
-  ```
-  versus
-  ``` 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 helps you to make your type
-  synchronous.
-*/
-
-export default function Utils (Y) {
-  Y.utils = {}
-
-  Y.utils.bubbleEvent = function (type, event) {
-    type.eventHandler.callEventListeners(event)
-    event.path = []
-    while (type != null && type._deepEventHandler != null) {
-      type._deepEventHandler.callEventListeners(event)
-      var parent = null
-      if (type._parent != null) {
-        parent = type.os.getType(type._parent)
-      }
-      if (parent != null && parent._getPathToChild != null) {
-        event.path = [parent._getPathToChild(type._model)].concat(event.path)
-        type = parent
-      } else {
-        type = null
-      }
-    }
-  }
-
-  class NamedEventHandler {
-    constructor () {
-      this._eventListener = {}
-    }
-    on (name, f) {
-      if (this._eventListener[name] == null) {
-        this._eventListener[name] = []
-      }
-      this._eventListener[name].push(f)
-    }
-    off (name, f) {
-      if (name == null || f == null) {
-        throw new Error('You must specify event name and function!')
-      }
-      let listener = this._eventListener[name] || []
-      this._eventListener[name] = listener.filter(e => e !== f)
-    }
-    emit (name, value) {
-      (this._eventListener[name] || []).forEach(l => l(value))
-    }
-    destroy () {
-      this._eventListener = null
-    }
-  }
-  Y.utils.NamedEventHandler = NamedEventHandler
-
-  class EventListenerHandler {
-    constructor () {
-      this.eventListeners = []
-    }
-    destroy () {
-      this.eventListeners = null
-    }
-     /*
-      Basic event listener boilerplate...
-    */
-    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 = 0; i < this.eventListeners.length; i++) {
-        try {
-          var _event = {}
-          for (var name in event) {
-            _event[name] = event[name]
-          }
-          this.eventListeners[i](_event)
-        } catch (e) {
-          /*
-            Your observer threw an error. This error was caught so that Yjs
-            can ensure data consistency! In order to debug this error you
-            have to check "Pause On Caught Exceptions" in developer tools.
-          */
-          console.error(e)
-        }
-      }
-    }
-  }
-  Y.utils.EventListenerHandler = EventListenerHandler
-
-  class EventHandler extends EventListenerHandler {
-    /* ::
-    waiting: Array<Insertion | Deletion>;
-    awaiting: number;
-    onevent: Function;
-    eventListeners: Array<Function>;
-    */
-    /*
-      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 /* : Function */) {
-      super()
-      this.waiting = []
-      this.awaiting = 0
-      this.onevent = onevent
-    }
-    destroy () {
-      super.destroy()
-      this.waiting = null
-      this.onevent = null
-    }
-    /*
-      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 if (op.struct === 'Delete') {
-        var self = this
-        var checkDelete = function checkDelete (d) {
-          if (d.length == null) {
-            throw new Error('This shouldn\'t happen! d.length must be defined!')
-          }
-          // we check if o deletes something in self.waiting
-          // if so, we remove the deleted operation
-          for (var w = 0; w < self.waiting.length; w++) {
-            var i = self.waiting[w]
-            if (i.struct === 'Insert' && i.id[0] === d.target[0]) {
-              var iLength = i.hasOwnProperty('content') ? i.content.length : 1
-              var dStart = d.target[1]
-              var dEnd = d.target[1] + (d.length || 1)
-              var iStart = i.id[1]
-              var iEnd = i.id[1] + iLength
-              // Check if they don't overlap
-              if (iEnd <= dStart || dEnd <= iStart) {
-                // no overlapping
-                continue
-              }
-              // we check all overlapping cases. All cases:
-              /*
-                1)  iiiii
-                      ddddd
-                    --> modify i and d
-                2)  iiiiiii
-                      ddddd
-                    --> modify i, remove d
-                3)  iiiiiii
-                      ddd
-                    --> remove d, modify i, and create another i (for the right hand side)
-                4)  iiiii
-                    ddddddd
-                    --> remove i, modify d
-                5)  iiiiiii
-                    ddddddd
-                    --> remove both i and d (**)
-                6)  iiiiiii
-                    ddddd
-                    --> modify i, remove d
-                7)    iii
-                    ddddddd
-                    --> remove i, create and apply two d with checkDelete(d) (**)
-                8)    iiiii
-                    ddddddd
-                    --> remove i, modify d (**)
-                9)    iiiii
-                    ddddd
-                    --> modify i and d
-                (**) (also check if i contains content or type)
-              */
-              // TODO: I left some debugger statements, because I want to debug all cases once in production. REMEMBER END TODO
-              if (iStart < dStart) {
-                if (dStart < iEnd) {
-                  if (iEnd < dEnd) {
-                    // Case 1
-                    // remove the right part of i's content
-                    i.content.splice(dStart - iStart)
-                    // remove the start of d's deletion
-                    d.length = dEnd - iEnd
-                    d.target = [d.target[0], iEnd]
-                    continue
-                  } else if (iEnd === dEnd) {
-                    // Case 2
-                    i.content.splice(dStart - iStart)
-                    // remove d, we do that by simply ending this function
-                    return
-                  } else { // (dEnd < iEnd)
-                    // Case 3
-                    var newI = {
-                      id: [i.id[0], dEnd],
-                      content: i.content.slice(dEnd - iStart),
-                      struct: 'Insert'
-                    }
-                    self.waiting.push(newI)
-                    i.content.splice(dStart - iStart)
-                    return
-                  }
-                }
-              } else if (dStart === iStart) {
-                if (iEnd < dEnd) {
-                  // Case 4
-                  d.length = dEnd - iEnd
-                  d.target = [d.target[0], iEnd]
-                  i.content = []
-                  continue
-                } else if (iEnd === dEnd) {
-                  // Case 5
-                  self.waiting.splice(w, 1)
-                  return
-                } else { // (dEnd < iEnd)
-                  // Case 6
-                  i.content = i.content.slice(dEnd - iStart)
-                  i.id = [i.id[0], dEnd]
-                  return
-                }
-              } else { // (dStart < iStart)
-                if (iStart < dEnd) {
-                  // they overlap
-                  /*
-                  7)    iii
-                      ddddddd
-                      --> remove i, create and apply two d with checkDelete(d) (**)
-                  8)    iiiii
-                      ddddddd
-                      --> remove i, modify d (**)
-                  9)    iiiii
-                      ddddd
-                      --> modify i and d
-                  */
-                  if (iEnd < dEnd) {
-                    // Case 7
-                    // debugger // TODO: You did not test this case yet!!!! (add the debugger here)
-                    self.waiting.splice(w, 1)
-                    checkDelete({
-                      target: [d.target[0], dStart],
-                      length: iStart - dStart,
-                      struct: 'Delete'
-                    })
-                    checkDelete({
-                      target: [d.target[0], iEnd],
-                      length: iEnd - dEnd,
-                      struct: 'Delete'
-                    })
-                    return
-                  } else if (iEnd === dEnd) {
-                    // Case 8
-                    self.waiting.splice(w, 1)
-                    w--
-                    d.length -= iLength
-                    continue
-                  } else { // dEnd < iEnd
-                    // Case 9
-                    d.length = iStart - dStart
-                    i.content.splice(0, dEnd - iStart)
-                    i.id = [i.id[0], dEnd]
-                    continue
-                  }
-                }
-              }
-            }
-          }
-          // finished with remaining operations
-          self.waiting.push(d)
-        }
-        if (op.key == null) {
-          // deletes in list
-          checkDelete(op)
-        } else {
-          // deletes in map
-          this.waiting.push(op)
-        }
-      } else {
-        this.waiting.push(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++
-      ops.map(Y.utils.copyOperation).forEach(this.onevent)
-    }
-    * awaitOps (transaction, f, args) {
-      function notSoSmartSort (array) {
-        // this function sorts insertions in a executable order
-        var result = []
-        while (array.length > 0) {
-          for (var i = 0; i < array.length; i++) {
-            var independent = true
-            for (var j = 0; j < array.length; j++) {
-              if (Y.utils.matchesId(array[j], array[i].left)) {
-                // array[i] depends on array[j]
-                independent = false
-                break
-              }
-            }
-            if (independent) {
-              result.push(array.splice(i, 1)[0])
-              i--
-            }
-          }
-        }
-        return result
-      }
-      var before = this.waiting.length
-      // somehow create new operations
-      yield * f.apply(transaction, args)
-      // remove all appended ops / awaited ops
-      this.waiting.splice(before)
-      if (this.awaiting > 0) this.awaiting--
-      // if there are no awaited ops anymore, we can update all waiting ops, and send execute them (if there are still no awaited ops)
-      if (this.awaiting === 0 && this.waiting.length > 0) {
-        // update all waiting ops
-        for (let i = 0; i < this.waiting.length; i++) {
-          var o = this.waiting[i]
-          if (o.struct === 'Insert') {
-            var _o = yield * transaction.getInsertion(o.id)
-            if (_o.parentSub != null && _o.left != null) {
-              // if o is an insertion of a map struc (parentSub is defined), then it shouldn't be necessary to compute left
-              this.waiting.splice(i, 1)
-              i-- // update index
-            } else if (!Y.utils.compareIds(_o.id, o.id)) {
-              // o got extended
-              o.left = [o.id[0], o.id[1] - 1]
-            } else if (_o.left == null) {
-              o.left = null
-            } else {
-              // find next undeleted op
-              var left = yield * transaction.getInsertion(_o.left)
-              while (left.deleted != null) {
-                if (left.left != null) {
-                  left = yield * transaction.getInsertion(left.left)
-                } else {
-                  left = null
-                  break
-                }
-              }
-              o.left = left != null ? Y.utils.getLastId(left) : null
-            }
-          }
-        }
-        // the previous stuff was async, so we have to check again!
-        // We also pull changes from the bindings, if there exists such a method, this could increase awaiting too
-        if (this._pullChanges != null) {
-          this._pullChanges()
-        }
-        if (this.awaiting === 0) {
-          // sort by type, execute inserts first
-          var ins = []
-          var dels = []
-          this.waiting.forEach(function (o) {
-            if (o.struct === 'Delete') {
-              dels.push(o)
-            } else {
-              ins.push(o)
-            }
-          })
-          this.waiting = []
-          // put in executable order
-          ins = notSoSmartSort(ins)
-          // this.onevent can trigger the creation of another operation
-          // -> check if this.awaiting increased & stop computation if it does
-          for (var i = 0; i < ins.length; i++) {
-            if (this.awaiting === 0) {
-              this.onevent(ins[i])
-            } else {
-              this.waiting = this.waiting.concat(ins.slice(i))
-              break
-            }
-          }
-          for (i = 0; i < dels.length; i++) {
-            if (this.awaiting === 0) {
-              this.onevent(dels[i])
-            } else {
-              this.waiting = this.waiting.concat(dels.slice(i))
-              break
-            }
-          }
-        }
-      }
-    }
-    // TODO: Remove awaitedInserts and awaitedDeletes in favor of awaitedOps, as they are deprecated and do not always work
-    // Do this in one of the coming releases that are breaking anyway
-    /*
-      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]
-        if (op.struct === 'Insert') {
-          for (var i = this.waiting.length - 1; i >= 0; i--) {
-            let w = this.waiting[i]
-            // TODO: do I handle split operations correctly here? Super unlikely, but yeah..
-            // Also: can this case happen? Can op be inserted in the middle of a larger op that is in $waiting?
-            if (w.struct === 'Insert') {
-              if (Y.utils.matchesId(w, op.left)) {
-                // 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(w.id, op.right)) {
-                // similar..
-                w.left = Y.utils.getLastId(op)
-                op.right = w.right
-              }
-            }
-          }
-        } else {
-          throw new Error('Expected Insert Operation!')
-        }
-      }
-      this._tryCallEvents(n)
-    }
-    /*
-      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 = 0; j < ops.length; j++) {
-        var del = ops[j]
-        if (del.struct === 'Delete') {
-          if (newLeft != null) {
-            for (var i = 0; i < this.waiting.length; i++) {
-              let w = this.waiting[i]
-              // We will just care about w.left
-              if (w.struct === 'Insert' && Y.utils.compareIds(del.target, w.left)) {
-                w.left = newLeft
-              }
-            }
-          }
-        } else {
-          throw new Error('Expected Delete Operation!')
-        }
-      }
-      this._tryCallEvents(n)
-    }
-    /* (private)
-      Try to execute the events for the waiting operations
-    */
-    _tryCallEvents () {
-      function notSoSmartSort (array) {
-        var result = []
-        while (array.length > 0) {
-          for (var i = 0; i < array.length; i++) {
-            var independent = true
-            for (var j = 0; j < array.length; j++) {
-              if (Y.utils.matchesId(array[j], array[i].left)) {
-                // array[i] depends on array[j]
-                independent = false
-                break
-              }
-            }
-            if (independent) {
-              result.push(array.splice(i, 1)[0])
-              i--
-            }
-          }
-        }
-        return result
-      }
-      if (this.awaiting > 0) this.awaiting--
-      if (this.awaiting === 0 && this.waiting.length > 0) {
-        var ins = []
-        var dels = []
-        this.waiting.forEach(function (o) {
-          if (o.struct === 'Delete') {
-            dels.push(o)
-          } else {
-            ins.push(o)
-          }
-        })
-        ins = notSoSmartSort(ins)
-        ins.forEach(this.onevent)
-        dels.forEach(this.onevent)
-        this.waiting = []
-      }
-    }
-  }
-  Y.utils.EventHandler = EventHandler
-
-  /*
-    Default class of custom types!
-  */
-  class CustomType {
-    getPath () {
-      var parent = null
-      if (this._parent != null) {
-        parent = this.os.getType(this._parent)
-      }
-      if (parent != null && parent._getPathToChild != null) {
-        var firstKey = parent._getPathToChild(this._model)
-        var parentKeys = parent.getPath()
-        parentKeys.push(firstKey)
-        return parentKeys
-      } else {
-        return []
-      }
-    }
-  }
-  Y.utils.CustomType = CustomType
-
-  /*
-    A wrapper for the definition of a custom type.
-    Every custom type must have three properties:
-
-    * struct
-      - Structname of this 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 CustomTypeDefinition { // eslint-disable-line
-    /* ::
-    struct: any;
-    initType: any;
-    class: Function;
-    name: String;
-    */
-    constructor (def) {
-      if (def.struct == null ||
-        def.initType == null ||
-        def.class == null ||
-        def.name == null ||
-        def.createType == null
-      ) {
-        throw new Error('Custom type was not initialized correctly!')
-      }
-      this.struct = def.struct
-      this.initType = def.initType
-      this.createType = def.createType
-      this.class = def.class
-      this.name = def.name
-      if (def.appendAdditionalInfo != null) {
-        this.appendAdditionalInfo = def.appendAdditionalInfo
-      }
-      this.parseArguments = (def.parseArguments || function () {
-        return [this]
-      }).bind(this)
-      this.parseArguments.typeDefinition = this
-    }
-  }
-  Y.utils.CustomTypeDefinition = CustomTypeDefinition
-
-  Y.utils.isTypeDefinition = function isTypeDefinition (v) {
-    if (v != null) {
-      if (v instanceof Y.utils.CustomTypeDefinition) return [v]
-      else if (v.constructor === Array && v[0] instanceof Y.utils.CustomTypeDefinition) return v
-      else if (v instanceof Function && v.typeDefinition instanceof Y.utils.CustomTypeDefinition) return [v.typeDefinition]
-    }
-    return false
-  }
-
-  /*
-    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
-
-  /*
-    Copy an operation, so that it can be manipulated.
-    Note: You must not change subproperties (except o.content)!
-  */
-  function copyOperation (o) {
-    o = copyObject(o)
-    if (o.content != null) {
-      o.content = o.content.map(function (c) { return c })
-    }
-    return o
-  }
-
-  Y.utils.copyOperation = copyOperation
-
-  /*
-    Defines a smaller relation on Id's
-  */
-  function smaller (a, b) {
-    return a[0] < b[0] || (a[0] === b[0] && (a[1] < b[1] || typeof a[1] < typeof b[1]))
-  }
-  Y.utils.smaller = smaller
-
-  function inDeletionRange (del, ins) {
-    return del.target[0] === ins[0] && del.target[1] <= ins[1] && ins[1] < del.target[1] + (del.length || 1)
-  }
-  Y.utils.inDeletionRange = inDeletionRange
-
-  function compareIds (id1, id2) {
-    if (id1 == null || id2 == null) {
-      return id1 === id2
-    } else {
-      return id1[0] === id2[0] && id1[1] === id2[1]
-    }
-  }
-  Y.utils.compareIds = compareIds
-
-  function matchesId (op, id) {
-    if (id == null || op == null) {
-      return id === op
-    } else {
-      if (id[0] === op.id[0]) {
-        if (op.content == null) {
-          return id[1] === op.id[1]
-        } else {
-          return id[1] >= op.id[1] && id[1] < op.id[1] + op.content.length
-        }
-      }
-    }
-    return false
-  }
-  Y.utils.matchesId = matchesId
-
-  function getLastId (op) {
-    if (op.content == null || op.content.length === 1) {
-      return op.id
-    } else {
-      return [op.id[0], op.id[1] + op.content.length - 1]
-    }
-  }
-  Y.utils.getLastId = getLastId
-
-  function createEmptyOpsArray (n) {
-    var a = new Array(n)
-    for (var i = 0; i < a.length; i++) {
-      a[i] = {
-        id: [null, null]
-      }
-    }
-    return a
-  }
-
-  function createSmallLookupBuffer (Store) {
-    /*
-      This buffer implements a very small buffer that temporarily stores operations
-      after they are read / before they are written.
-      The buffer basically implements FIFO. Often requested lookups will be re-queued every time they are looked up / written.
-
-      It can speed up lookups on Operation Stores and State Stores. But it does not require notable use of memory or processing power.
-
-      Good for os and ss, bot not for ds (because it often uses methods that require a flush)
-
-      I tried to optimize this for performance, therefore no highlevel operations.
-    */
-    class SmallLookupBuffer extends Store {
-      constructor (arg1, arg2) {
-        // super(...arguments) -- do this when this is supported by stable nodejs
-        super(arg1, arg2)
-        this.writeBuffer = createEmptyOpsArray(5)
-        this.readBuffer = createEmptyOpsArray(10)
-      }
-      * find (id, noSuperCall) {
-        var i, r
-        for (i = this.readBuffer.length - 1; i >= 0; i--) {
-          r = this.readBuffer[i]
-          // we don't have to use compareids, because id is always defined!
-          if (r.id[1] === id[1] && r.id[0] === id[0]) {
-            // found r
-            // move r to the end of readBuffer
-            for (; i < this.readBuffer.length - 1; i++) {
-              this.readBuffer[i] = this.readBuffer[i + 1]
-            }
-            this.readBuffer[this.readBuffer.length - 1] = r
-            return r
-          }
-        }
-        var o
-        for (i = this.writeBuffer.length - 1; i >= 0; i--) {
-          r = this.writeBuffer[i]
-          if (r.id[1] === id[1] && r.id[0] === id[0]) {
-            o = r
-            break
-          }
-        }
-        if (i < 0 && noSuperCall === undefined) {
-          // did not reach break in last loop
-          // read id and put it to the end of readBuffer
-          o = yield * super.find(id)
-        }
-        if (o != null) {
-          for (i = 0; i < this.readBuffer.length - 1; i++) {
-            this.readBuffer[i] = this.readBuffer[i + 1]
-          }
-          this.readBuffer[this.readBuffer.length - 1] = o
-        }
-        return o
-      }
-      * put (o) {
-        var id = o.id
-        var i, r // helper variables
-        for (i = this.writeBuffer.length - 1; i >= 0; i--) {
-          r = this.writeBuffer[i]
-          if (r.id[1] === id[1] && r.id[0] === id[0]) {
-            // is already in buffer
-            // forget r, and move o to the end of writeBuffer
-            for (; i < this.writeBuffer.length - 1; i++) {
-              this.writeBuffer[i] = this.writeBuffer[i + 1]
-            }
-            this.writeBuffer[this.writeBuffer.length - 1] = o
-            break
-          }
-        }
-        if (i < 0) {
-          // did not reach break in last loop
-          // write writeBuffer[0]
-          var write = this.writeBuffer[0]
-          if (write.id[0] !== null) {
-            yield * super.put(write)
-          }
-          // put o to the end of writeBuffer
-          for (i = 0; i < this.writeBuffer.length - 1; i++) {
-            this.writeBuffer[i] = this.writeBuffer[i + 1]
-          }
-          this.writeBuffer[this.writeBuffer.length - 1] = o
-        }
-        // check readBuffer for every occurence of o.id, overwrite if found
-        // whether found or not, we'll append o to the readbuffer
-        for (i = 0; i < this.readBuffer.length - 1; i++) {
-          r = this.readBuffer[i + 1]
-          if (r.id[1] === id[1] && r.id[0] === id[0]) {
-            this.readBuffer[i] = o
-          } else {
-            this.readBuffer[i] = r
-          }
-        }
-        this.readBuffer[this.readBuffer.length - 1] = o
-      }
-      * delete (id) {
-        var i, r
-        for (i = 0; i < this.readBuffer.length; i++) {
-          r = this.readBuffer[i]
-          if (r.id[1] === id[1] && r.id[0] === id[0]) {
-            this.readBuffer[i] = {
-              id: [null, null]
-            }
-          }
-        }
-        yield * this.flush()
-        yield * super.delete(id)
-      }
-      * findWithLowerBound (id) {
-        var o = yield * this.find(id, true)
-        if (o != null) {
-          return o
-        } else {
-          yield * this.flush()
-          return yield * super.findWithLowerBound.apply(this, arguments)
-        }
-      }
-      * findWithUpperBound (id) {
-        var o = yield * this.find(id, true)
-        if (o != null) {
-          return o
-        } else {
-          yield * this.flush()
-          return yield * super.findWithUpperBound.apply(this, arguments)
-        }
-      }
-      * findNext () {
-        yield * this.flush()
-        return yield * super.findNext.apply(this, arguments)
-      }
-      * findPrev () {
-        yield * this.flush()
-        return yield * super.findPrev.apply(this, arguments)
-      }
-      * iterate () {
-        yield * this.flush()
-        yield * super.iterate.apply(this, arguments)
-      }
-      * flush () {
-        for (var i = 0; i < this.writeBuffer.length; i++) {
-          var write = this.writeBuffer[i]
-          if (write.id[0] !== null) {
-            yield * super.put(write)
-            this.writeBuffer[i] = {
-              id: [null, null]
-            }
-          }
-        }
-      }
-    }
-    return SmallLookupBuffer
-  }
-  Y.utils.createSmallLookupBuffer = createSmallLookupBuffer
-
-  // Generates a unique id, for use as a user id.
-  // Thx to @jed for this script https://gist.github.com/jed/982883
-  function generateGuid(a){return a?(a^Math.random()*16>>a/4).toString(16):([1e7]+-1e3+-4e3+-8e3+-1e11).replace(/[018]/g,generateGuid)} // eslint-disable-line
-  Y.utils.generateGuid = generateGuid
-}
--- a/src/index.js
+++ b/src/index.js
@@ -0,0 +1,62 @@
+
+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,
+  YEvent,
+  Item,
+  AbstractStruct,
+  GC,
+  ContentBinary,
+  ContentDeleted,
+  ContentEmbed,
+  ContentFormat,
+  ContentJSON,
+  ContentAny,
+  ContentString,
+  ContentType,
+  AbstractType,
+  RelativePosition,
+  createRelativePositionFromTypeIndex,
+  createRelativePositionFromJSON,
+  createAbsolutePositionFromRelativePosition,
+  compareRelativePositions,
+  writeRelativePosition,
+  readRelativePosition,
+  ID,
+  createID,
+  compareIDs,
+  getState,
+  Snapshot,
+  createSnapshot,
+  createDeleteSet,
+  createDeleteSetFromStructStore,
+  snapshot,
+  emptySnapshot,
+  findRootTypeKey,
+  typeListToArraySnapshot,
+  typeMapGetSnapshot,
+  iterateDeletedStructs,
+  applyUpdate,
+  readUpdate,
+  encodeStateAsUpdate,
+  encodeStateVector,
+  UndoManager,
+  decodeSnapshot,
+  encodeSnapshot,
+  isDeleted,
+  isParentOf,
+  equalSnapshots,
+  PermanentUserData, // @TODO experimental
+  tryGc,
+  transact
+} from './internals.js'
--- a/src/internals.js
+++ b/src/internals.js
@@ -0,0 +1,36 @@
+
+export * from './utils/DeleteSet.js'
+export * from './utils/Doc.js'
+export * from './utils/encoding.js'
+export * from './utils/EventHandler.js'
+export * from './utils/ID.js'
+export * from './utils/isParentOf.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/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/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'
--- a/src/structs/AbstractStruct.js
+++ b/src/structs/AbstractStruct.js
@@ -0,0 +1,86 @@
+
+import {
+  StructStore, ID, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js' // eslint-disable-line
+import * as error from 'lib0/error.js'
+
+export class AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {number} length
+   */
+  constructor (id, length) {
+    /**
+     * The uniqe identifier of this struct.
+     * @type {ID}
+     * @readonly
+     */
+    this.id = id
+    this.length = length
+    this.deleted = false
+  }
+
+  /**
+   * 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 {encoding.Encoder} encoder The encoder to write data to.
+   * @param {number} offset
+   * @param {number} encodingRef
+   */
+  write (encoder, offset, encodingRef) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  integrate (transaction) {
+    throw error.methodUnimplemented()
+  }
+}
+
+export class AbstractStructRef {
+  /**
+   * @param {ID} id
+   */
+  constructor (id) {
+    /**
+     * @type {Array<ID>}
+     */
+    this._missing = []
+    /**
+     * The uniqe identifier of this type.
+     * @type {ID}
+     */
+    this.id = id
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @return {Array<ID|null>}
+   */
+  getMissing (transaction) {
+    return this._missing
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @param {number} offset
+   * @return {AbstractStruct}
+   */
+  toStruct (transaction, store, offset) {
+    throw error.methodUnimplemented()
+  }
+}
--- a/src/structs/ContentAny.js
+++ b/src/structs/ContentAny.js
@@ -0,0 +1,111 @@
+import {
+  Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoding.writeVarUint(encoder, len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoding.writeAny(encoder, c)
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 8
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {ContentAny}
+ */
+export const readContentAny = decoder => {
+  const len = decoding.readVarUint(decoder)
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    cs.push(decoding.readAny(decoder))
+  }
+  return new ContentAny(cs)
+}
--- a/src/structs/ContentBinary.js
+++ b/src/structs/ContentBinary.js
@@ -0,0 +1,95 @@
+import {
+  StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as buffer from 'lib0/buffer.js'
+import * as error from 'lib0/error.js'
+
+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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeVarUint8Array(encoder, this.content)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 3
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {ContentBinary}
+ */
+export const readContentBinary = decoder => new ContentBinary(buffer.copyUint8Array(decoding.readVarUint8Array(decoder)))
--- a/src/structs/ContentDeleted.js
+++ b/src/structs/ContentDeleted.js
@@ -0,0 +1,104 @@
+
+import {
+  addToDeleteSet,
+  StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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, this.len)
+    item.deleted = true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeVarUint(encoder, this.len - offset)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 1
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ContentDeleted}
+ */
+export const readContentDeleted = decoder => new ContentDeleted(decoding.readVarUint(decoder))
--- a/src/structs/ContentEmbed.js
+++ b/src/structs/ContentEmbed.js
@@ -0,0 +1,100 @@
+
+import {
+  StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as error from 'lib0/error.js'
+
+/**
+ * @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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeVarString(encoder, JSON.stringify(this.embed))
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 5
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ContentEmbed}
+ */
+export const readContentEmbed = decoder => new ContentEmbed(JSON.parse(decoding.readVarString(decoder)))
--- a/src/structs/ContentFormat.js
+++ b/src/structs/ContentFormat.js
@@ -0,0 +1,101 @@
+
+import {
+  Item, StructStore, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as error from 'lib0/error.js'
+
+/**
+ * @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) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeVarString(encoder, this.key)
+    encoding.writeVarString(encoder, JSON.stringify(this.value))
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 6
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {ContentFormat}
+ */
+export const readContentFormat = decoder => new ContentFormat(decoding.readVarString(decoder), JSON.parse(decoding.readVarString(decoder)))
--- a/src/structs/ContentJSON.js
+++ b/src/structs/ContentJSON.js
@@ -0,0 +1,121 @@
+import {
+  Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoding.writeVarUint(encoder, len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoding.writeVarString(encoder, c === undefined ? 'undefined' : JSON.stringify(c))
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 2
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ContentJSON}
+ */
+export const readContentJSON = decoder => {
+  const len = decoding.readVarUint(decoder)
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    const c = decoding.readVarString(decoder)
+    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 +1,104 @@
+import {
+  Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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)
+    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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeVarString(encoder, offset === 0 ? this.str : this.str.slice(offset))
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 4
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ContentString}
+ */
+export const readContentString = decoder => new ContentString(decoding.readVarString(decoder))
--- a/src/structs/ContentType.js
+++ b/src/structs/ContentType.js
@@ -0,0 +1,174 @@
+
+import {
+  readYArray,
+  readYMap,
+  readYText,
+  readYXmlElement,
+  readYXmlFragment,
+  readYXmlHook,
+  readYXmlText,
+  StructStore, Transaction, Item, YEvent, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js' // eslint-disable-line
+import * as decoding from 'lib0/decoding.js'
+import * as error from 'lib0/error.js'
+
+/**
+ * @type {Array<function(decoding.Decoder):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.add(item.id)
+      }
+      item = item.right
+    }
+    this.type._map.forEach(item => {
+      if (!item.deleted) {
+        item.delete(transaction)
+      } else {
+        // same as above
+        transaction._mergeStructs.add(item.id)
+      }
+    })
+    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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    this.type._write(encoder)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 7
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ContentType}
+ */
+export const readContentType = decoder => new ContentType(typeRefs[decoding.readVarUint(decoder)](decoder))
--- a/src/structs/GC.js
+++ b/src/structs/GC.js
@@ -0,0 +1,90 @@
+
+import {
+  AbstractStructRef,
+  AbstractStruct,
+  createID,
+  addStruct,
+  StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding.js'
+import * as encoding from 'lib0/encoding.js'
+
+export const structGCRefNumber = 0
+
+/**
+ * @private
+ */
+export class GC extends AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {number} length
+   */
+  constructor (id, length) {
+    super(id, length)
+    this.deleted = true
+  }
+
+  delete () {}
+
+  /**
+   * @param {GC} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.length += right.length
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  integrate (transaction) {
+    addStruct(transaction.doc.store, this)
+  }
+
+  /**
+   * @param {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoding.writeUint8(encoder, structGCRefNumber)
+    encoding.writeVarUint(encoder, this.length - offset)
+  }
+}
+
+/**
+ * @private
+ */
+export class GCRef extends AbstractStructRef {
+  /**
+   * @param {decoding.Decoder} decoder
+   * @param {ID} id
+   * @param {number} info
+   */
+  constructor (decoder, id, info) {
+    super(id)
+    /**
+     * @type {number}
+     */
+    this.length = decoding.readVarUint(decoder)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @param {number} offset
+   * @return {GC}
+   */
+  toStruct (transaction, store, offset) {
+    if (offset > 0) {
+      // @ts-ignore
+      this.id = createID(this.id.client, this.id.clock + offset)
+      this.length -= offset
+    }
+    return new GC(
+      this.id,
+      this.length
+    )
+  }
+}
--- a/src/structs/Item.js
+++ b/src/structs/Item.js
@@ -0,0 +1,778 @@
+
+import {
+  readID,
+  createID,
+  writeID,
+  GC,
+  nextID,
+  AbstractStructRef,
+  AbstractStruct,
+  replaceStruct,
+  addStruct,
+  addToDeleteSet,
+  findRootTypeKey,
+  compareIDs,
+  getItem,
+  getItemCleanEnd,
+  getItemCleanStart,
+  readContentDeleted,
+  readContentBinary,
+  readContentJSON,
+  readContentAny,
+  readContentString,
+  readContentEmbed,
+  readContentFormat,
+  readContentType,
+  addChangedTypeToTransaction,
+  ContentType, ContentDeleted, StructStore, ID, AbstractType, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error.js'
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as maplib from 'lib0/map.js'
+import * as set from 'lib0/set.js'
+import * as binary from 'lib0/binary.js'
+
+/**
+ * @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 = 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) => {
+  const id = leftItem.id
+  // create rightItem
+  const rightItem = new Item(
+    createID(id.client, id.clock + diff),
+    leftItem,
+    createID(id.client, id.clock + diff - 1),
+    leftItem.right,
+    leftItem.rightOrigin,
+    leftItem.parent,
+    leftItem.parentSub,
+    leftItem.content.splice(diff)
+  )
+  if (leftItem.deleted) {
+    rightItem.deleted = true
+  }
+  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.add(rightItem.id)
+  // update parent._map
+  if (rightItem.parentSub !== null && rightItem.right === null) {
+    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
+ *
+ * @return {Item|null}
+ *
+ * @private
+ */
+export const redoItem = (transaction, item, redoitems) => {
+  if (item.redone !== null) {
+    return getItemCleanStart(transaction, item.redone)
+  }
+  let parentItem = 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 !== transaction.doc.clientID) {
+        // 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} */ (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) === 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 && leftTrace.parent._item !== parentItem) {
+        leftTrace = leftTrace.redone === null ? null : getItemCleanStart(transaction, leftTrace.redone)
+      }
+      if (leftTrace !== null && 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 && rightTrace.parent._item !== parentItem) {
+        rightTrace = rightTrace.redone === null ? null : getItemCleanStart(transaction, rightTrace.redone)
+      }
+      if (rightTrace !== null && rightTrace.parent._item === parentItem) {
+        right = rightTrace
+        break
+      }
+      right = right.right
+    }
+  }
+  const redoneItem = new Item(
+    nextID(transaction),
+    left, left === null ? null : left.lastId,
+    right, right === null ? null : right.id,
+    parentItem === null ? item.parent : /** @type {ContentType} */ (parentItem.content).type,
+    item.parentSub,
+    item.content.copy()
+  )
+  item.redone = redoneItem.id
+  keepItem(redoneItem, true)
+  redoneItem.integrate(transaction)
+  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>} parent
+   * @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}
+     * @readonly
+     */
+    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.
+     * @readonly
+     * @type {ID | null}
+     */
+    this.rightOrigin = rightOrigin
+    /**
+     * The parent type.
+     * @type {AbstractType<any>}
+     * @readonly
+     */
+    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}
+     * @readonly
+     */
+    this.parentSub = parentSub
+    /**
+     * Whether this item was deleted or not.
+     * @type {Boolean}
+     */
+    this.deleted = false
+    /**
+     * 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
+    this.length = content.getLength()
+    this.countable = content.isCountable()
+    /**
+     * If true, do not garbage collect this Item.
+     */
+    this.keep = false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  integrate (transaction) {
+    const store = transaction.doc.store
+    const id = this.id
+    const parent = this.parent
+    const parentSub = this.parentSub
+    const length = this.length
+    /**
+     * @type {Item|null}
+     */
+    let o
+    // set o to the first conflicting item
+    if (this.left !== null) {
+      o = this.left.right
+    } else if (parentSub !== null) {
+      o = parent._map.get(parentSub) || null
+      while (o !== null && o.left !== null) {
+        o = o.left
+      }
+    } else {
+      o = parent._start
+    }
+    // TODO: use something like DeleteSet here (a tree implementation would be best)
+    /**
+     * @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 < id.client) {
+          this.left = o
+          conflictingItems.clear()
+        }
+      } else if (o.origin !== null && itemsBeforeOrigin.has(getItem(store, o.origin))) {
+        // case 2
+        if (o.origin === null || !conflictingItems.has(getItem(store, o.origin))) {
+          this.left = o
+          conflictingItems.clear()
+        }
+      } else {
+        break
+      }
+      o = o.right
+    }
+    // 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 (parentSub !== null) {
+        r = parent._map.get(parentSub) || null
+        while (r !== null && r.left !== null) {
+          r = r.left
+        }
+      } else {
+        r = parent._start
+        parent._start = this
+      }
+      this.right = r
+    }
+    if (this.right !== null) {
+      this.right.left = this
+    } else if (parentSub !== null) {
+      // set as current parent value if right === null and this is parentSub
+      parent._map.set(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 (parentSub === null && this.countable && !this.deleted) {
+      parent._length += length
+    }
+    addStruct(store, this)
+    this.content.integrate(transaction, this)
+    // add parent to transaction.changed
+    addChangedTypeToTransaction(transaction, parent, parentSub)
+    if ((parent._item !== null && parent._item.deleted) || (this.right !== null && parentSub !== null)) {
+      // delete if parent is deleted or if this is not the current attribute value of parent
+      this.delete(transaction)
+    }
+  }
+
+  /**
+   * 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 () {
+    return createID(this.id.client, this.id.clock + this.length - 1)
+  }
+
+  /**
+   * Try to merge two items
+   *
+   * @param {Item} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (
+      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)
+    ) {
+      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 = this.parent
+      // adjust the length of parent
+      if (this.countable && this.parentSub === null) {
+        parent._length -= this.length
+      }
+      this.deleted = true
+      addToDeleteSet(transaction.deleteSet, this.id, this.length)
+      maplib.setIfUndefined(transaction.changed, parent, set.create).add(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 {encoding.Encoder} 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
+    encoding.writeUint8(encoder, info)
+    if (origin !== null) {
+      writeID(encoder, origin)
+    }
+    if (rightOrigin !== null) {
+      writeID(encoder, rightOrigin)
+    }
+    if (origin === null && rightOrigin === null) {
+      const parent = this.parent
+      if (parent._item === null) {
+        // parent type on y._map
+        // find the correct key
+        const ykey = findRootTypeKey(parent)
+        encoding.writeVarUint(encoder, 1) // write parentYKey
+        encoding.writeVarString(encoder, ykey)
+      } else {
+        encoding.writeVarUint(encoder, 0) // write parent id
+        writeID(encoder, parent._item.id)
+      }
+      if (parentSub !== null) {
+        encoding.writeVarString(encoder, parentSub)
+      }
+    }
+    this.content.write(encoder, offset)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @param {number} info
+ */
+const readItemContent = (decoder, info) => contentRefs[info & binary.BITS5](decoder)
+
+/**
+ * A lookup map for reading Item content.
+ *
+ * @type {Array<function(decoding.Decoder):AbstractContent>}
+ */
+export const contentRefs = [
+  () => { throw error.unexpectedCase() }, // GC is not ItemContent
+  readContentDeleted,
+  readContentJSON,
+  readContentBinary,
+  readContentString,
+  readContentEmbed,
+  readContentFormat,
+  readContentType,
+  readContentAny
+]
+
+/**
+ * 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 {encoding.Encoder} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    throw error.methodUnimplemented()
+  }
+}
+
+/**
+ * @private
+ */
+export class ItemRef extends AbstractStructRef {
+  /**
+   * @param {decoding.Decoder} decoder
+   * @param {ID} id
+   * @param {number} info
+   */
+  constructor (decoder, id, info) {
+    super(id)
+    /**
+     * The item that was originally to the left of this item.
+     * @type {ID | null}
+     */
+    this.left = (info & binary.BIT8) === binary.BIT8 ? readID(decoder) : null
+    /**
+     * The item that was originally to the right of this item.
+     * @type {ID | null}
+     */
+    this.right = (info & binary.BIT7) === binary.BIT7 ? readID(decoder) : null
+    const canCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+    const hasParentYKey = canCopyParentInfo ? decoding.readVarUint(decoder) === 1 : 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}
+     */
+    this.parentYKey = canCopyParentInfo && hasParentYKey ? decoding.readVarString(decoder) : null
+    /**
+     * The parent type.
+     * @type {ID | null}
+     */
+    this.parent = canCopyParentInfo && !hasParentYKey ? readID(decoder) : null
+    /**
+     * 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 = canCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoding.readVarString(decoder) : null
+    const missing = this._missing
+    if (this.left !== null) {
+      missing.push(this.left)
+    }
+    if (this.right !== null) {
+      missing.push(this.right)
+    }
+    if (this.parent !== null) {
+      missing.push(this.parent)
+    }
+    /**
+     * @type {AbstractContent}
+     */
+    this.content = readItemContent(decoder, info)
+    this.length = this.content.getLength()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @param {number} offset
+   * @return {Item|GC}
+   */
+  toStruct (transaction, store, offset) {
+    if (offset > 0) {
+      /**
+       * @type {ID}
+       */
+      const id = this.id
+      this.id = createID(id.client, id.clock + offset)
+      this.left = createID(this.id.client, this.id.clock - 1)
+      this.content = this.content.splice(offset)
+      this.length -= offset
+    }
+
+    const left = this.left === null ? null : getItemCleanEnd(transaction, store, this.left)
+    const right = this.right === null ? null : getItemCleanStart(transaction, this.right)
+    let parent = null
+    let parentSub = this.parentSub
+    if (this.parent !== null) {
+      const parentItem = getItem(store, this.parent)
+      // Edge case: toStruct is called with an offset > 0. In this case left is defined.
+      // Depending in which order structs arrive, left may be GC'd and the parent not
+      // deleted. This is why we check if left is GC'd. Strictly we don't have
+      // to check if right is GC'd, but we will in case we run into future issues
+      if (!parentItem.deleted && (left === null || left.constructor !== GC) && (right === null || right.constructor !== GC)) {
+        parent = /** @type {ContentType} */ (parentItem.content).type
+      }
+    } else if (this.parentYKey !== null) {
+      parent = transaction.doc.get(this.parentYKey)
+    } else if (left !== null) {
+      if (left.constructor !== GC) {
+        parent = left.parent
+        parentSub = left.parentSub
+      }
+    } else if (right !== null) {
+      if (right.constructor !== GC) {
+        parent = right.parent
+        parentSub = right.parentSub
+      }
+    } else {
+      throw error.unexpectedCase()
+    }
+
+    return parent === null
+      ? new GC(this.id, this.length)
+      : new Item(
+        this.id,
+        left,
+        this.left,
+        right,
+        this.right,
+        parent,
+        parentSub,
+        this.content
+      )
+  }
+}
--- a/src/types/AbstractType.js
+++ b/src/types/AbstractType.js
@@ -0,0 +1,592 @@
+
+import {
+  removeEventHandlerListener,
+  callEventHandlerListeners,
+  addEventHandlerListener,
+  createEventHandler,
+  nextID,
+  isVisible,
+  ContentType,
+  ContentAny,
+  ContentBinary,
+  createID,
+  getItemCleanStart,
+  Doc, Snapshot, Transaction, EventHandler, YEvent, Item, // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map.js'
+import * as iterator from 'lib0/iterator.js'
+import * as error from 'lib0/error.js'
+import * as encoding from 'lib0/encoding.js' // eslint-disable-line
+
+/**
+ * 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._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()
+  }
+
+  /**
+   * 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()
+  }
+
+  /**
+   * @param {encoding.Encoder} 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) { /* skip if no type is specified */ }
+
+  /**
+   * 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
+ * @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) => {
+  for (let n = type._start; 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|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenericsAfter = (transaction, parent, referenceItem, content) => {
+  let left = referenceItem
+  const right = referenceItem === null ? parent._start : referenceItem.right
+  /**
+   * @type {Array<Object|Array<any>|number>}
+   */
+  let jsonContent = []
+  const packJsonContent = () => {
+    if (jsonContent.length > 0) {
+      left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentAny(jsonContent))
+      left.integrate(transaction)
+      jsonContent = []
+    }
+  }
+  content.forEach(c => {
+    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(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentBinary(new Uint8Array(/** @type {Uint8Array} */ (c))))
+            left.integrate(transaction)
+            break
+          default:
+            if (c instanceof AbstractType) {
+              left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentType(c))
+              left.integrate(transaction)
+            } else {
+              throw new Error('Unexpected content type in insert operation')
+            }
+        }
+    }
+  })
+  packJsonContent()
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @param {Array<Object<string,any>|Array<any>|number|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenerics = (transaction, parent, index, content) => {
+  if (index === 0) {
+    return typeListInsertGenericsAfter(transaction, parent, null, content)
+  }
+  let n = parent._start
+  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
+    }
+  }
+  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 }
+  let n = parent._start
+  // 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 error.create('array length exceeded')
+  }
+}
+
+/**
+ * @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|Array<any>|string|Uint8Array|AbstractType<any>} value
+ *
+ * @private
+ * @function
+ */
+export const typeMapSet = (transaction, parent, key, value) => {
+  const left = parent._map.get(key) || null
+  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
+      default:
+        if (value instanceof AbstractType) {
+          content = new ContentType(value)
+        } else {
+          throw new Error('Unexpected content type')
+        }
+    }
+  }
+  new Item(nextID(transaction), left, left === null ? null : left.lastId, null, null, parent, key, content).integrate(transaction)
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @return {Object<string,any>|number|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|Array<any>|string|Uint8Array|AbstractType<any>|undefined>}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetAll = (parent) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const res = {}
+  for (const [key, value] of parent._map) {
+    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|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 +1,211 @@
+/**
+ * @module YArray
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeListGet,
+  typeListToArray,
+  typeListForEach,
+  typeListCreateIterator,
+  typeListInsertGenerics,
+  typeListDelete,
+  typeListMap,
+  YArrayRefID,
+  callTypeObservers,
+  transact,
+  Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+import * as encoding from 'lib0/encoding.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 {IterableIterator<T>}
+ */
+export class YArray extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Array<any>?}
+     * @private
+     */
+    this._prelimContent = []
+  }
+
+  /**
+   * 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()
+  }
+
+  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) {
+    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)
+  }
+
+  /**
+   * 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 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 T,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 {encoding.Encoder} encoder
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YArrayRefID)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ *
+ * @private
+ * @function
+ */
+export const readYArray = decoder => new YArray()
--- a/src/types/YMap.js
+++ b/src/types/YMap.js
@@ -0,0 +1,226 @@
+
+/**
+ * @module YMap
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeMapDelete,
+  typeMapSet,
+  typeMapGet,
+  typeMapHas,
+  createMapIterator,
+  YMapRefID,
+  callTypeObservers,
+  transact,
+  Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+import * as iterator from 'lib0/iterator.js'
+
+/**
+ * @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 T number|string|Object|Array|Uint8Array
+ * A shared Map implementation.
+ *
+ * @extends AbstractType<YMapEvent<T>>
+ * @implements {IterableIterator}
+ */
+export class YMap extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Map<string,any>?}
+     * @private
+     */
+    this._prelimContent = new Map()
+  }
+
+  /**
+   * 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)
+    for (const [key, value] of /** @type {Map<string, any>} */ (this._prelimContent)) {
+      this.set(key, value)
+    }
+    this._prelimContent = null
+  }
+
+  _copy () {
+    return new YMap()
+  }
+
+  /**
+   * 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,T>}
+   */
+  toJSON () {
+    /**
+     * @type {Object<string,T>}
+     */
+    const map = {}
+    for (const [key, item] of this._map) {
+      if (!item.deleted) {
+        const v = item.content.getContent()[item.length - 1]
+        map[key] = v instanceof AbstractType ? v.toJSON() : v
+      }
+    }
+    return map
+  }
+
+  /**
+   * 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 keys for each element in the YMap Type.
+   *
+   * @return {IterableIterator<string>}
+   */
+  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 overy key-value pair.
+   *
+   * @param {function(T,string,YMap<T>):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    /**
+     * @type {Object<string,T>}
+     */
+    const map = {}
+    for (const [key, item] of this._map) {
+      if (!item.deleted) {
+        f(item.content.getContent()[item.length - 1], key, this)
+      }
+    }
+    return map
+  }
+
+  /**
+   * @return {IterableIterator<T>}
+   */
+  [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 {T} 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 {T|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)
+  }
+
+  /**
+   * @param {encoding.Encoder} encoder
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YMapRefID)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ *
+ * @private
+ * @function
+ */
+export const readYMap = decoder => new YMap()
--- a/src/types/YText.js
+++ b/src/types/YText.js
@@ -0,0 +1,948 @@
+
+/**
+ * @module YText
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  nextID,
+  createID,
+  getItemCleanStart,
+  isVisible,
+  YTextRefID,
+  callTypeObservers,
+  transact,
+  ContentEmbed,
+  ContentFormat,
+  ContentString,
+  splitSnapshotAffectedStructs,
+  ID, Doc, Item, Snapshot, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+import * as encoding from 'lib0/encoding.js'
+import * as object from 'lib0/object.js'
+
+/**
+ * @param {any} a
+ * @param {any} b
+ * @return {boolean}
+ */
+const equalAttrs = (a, b) => a === b || (typeof a === 'object' && typeof b === 'object' && a && b && object.equalFlat(a, b))
+
+export class ItemListPosition {
+  /**
+   * @param {Item|null} left
+   * @param {Item|null} right
+   */
+  constructor (left, right) {
+    this.left = left
+    this.right = right
+  }
+}
+
+export class ItemTextListPosition extends ItemListPosition {
+  /**
+   * @param {Item|null} left
+   * @param {Item|null} right
+   * @param {Map<string,any>} currentAttributes
+   */
+  constructor (left, right, currentAttributes) {
+    super(left, right)
+    this.currentAttributes = currentAttributes
+  }
+}
+
+export class ItemInsertionResult extends ItemListPosition {
+  /**
+   * @param {Item|null} left
+   * @param {Item|null} right
+   * @param {Map<string,any>} negatedAttributes
+   */
+  constructor (left, right, negatedAttributes) {
+    super(left, right)
+    this.negatedAttributes = negatedAttributes
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {Map<string,any>} currentAttributes
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {number} count
+ * @return {ItemTextListPosition}
+ *
+ * @private
+ * @function
+ */
+const findNextPosition = (transaction, currentAttributes, left, right, count) => {
+  while (right !== null && count > 0) {
+    switch (right.content.constructor) {
+      case ContentEmbed:
+      case ContentString:
+        if (!right.deleted) {
+          if (count < right.length) {
+            // split right
+            getItemCleanStart(transaction, createID(right.id.client, right.id.clock + count))
+          }
+          count -= right.length
+        }
+        break
+      case ContentFormat:
+        if (!right.deleted) {
+          updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (right.content))
+        }
+        break
+    }
+    left = right
+    right = right.right
+  }
+  return new ItemTextListPosition(left, right, currentAttributes)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @return {ItemTextListPosition}
+ *
+ * @private
+ * @function
+ */
+const findPosition = (transaction, parent, index) => {
+  const currentAttributes = new Map()
+  const right = parent._start
+  return findNextPosition(transaction, currentAttributes, null, right, index)
+}
+
+/**
+ * Negate applied formats
+ *
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} negatedAttributes
+ * @return {ItemListPosition}
+ *
+ * @private
+ * @function
+ */
+const insertNegatedAttributes = (transaction, parent, left, right, negatedAttributes) => {
+  // check if we really need to remove attributes
+  while (
+    right !== null && (
+      right.deleted === true || (
+        right.content.constructor === ContentFormat &&
+        equalAttrs(negatedAttributes.get(/** @type {ContentFormat} */ (right.content).key), /** @type {ContentFormat} */ (right.content).value)
+      )
+    )
+  ) {
+    if (!right.deleted) {
+      negatedAttributes.delete(/** @type {ContentFormat} */ (right.content).key)
+    }
+    left = right
+    right = right.right
+  }
+  for (const [key, val] of negatedAttributes) {
+    left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentFormat(key, val))
+    left.integrate(transaction)
+  }
+  return { left, right }
+}
+
+/**
+ * @param {Map<string,any>} currentAttributes
+ * @param {ContentFormat} format
+ *
+ * @private
+ * @function
+ */
+const updateCurrentAttributes = (currentAttributes, format) => {
+  const { key, value } = format
+  if (value === null) {
+    currentAttributes.delete(key)
+  } else {
+    currentAttributes.set(key, value)
+  }
+}
+
+/**
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} currentAttributes
+ * @param {Object<string,any>} attributes
+ * @return {ItemListPosition}
+ *
+ * @private
+ * @function
+ */
+const minimizeAttributeChanges = (left, right, currentAttributes, attributes) => {
+  // go right while attributes[right.key] === right.value (or right is deleted)
+  while (true) {
+    if (right === null) {
+      break
+    } else if (right.deleted) {
+      // continue
+    } else if (right.content.constructor === ContentFormat && equalAttrs(attributes[(/** @type {ContentFormat} */ (right.content)).key] || null, /** @type {ContentFormat} */ (right.content).value)) {
+      // found a format, update currentAttributes and continue
+      updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (right.content))
+    } else {
+      break
+    }
+    left = right
+    right = right.right
+  }
+  return new ItemListPosition(left, right)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} currentAttributes
+ * @param {Object<string,any>} attributes
+ * @return {ItemInsertionResult}
+ *
+ * @private
+ * @function
+ **/
+const insertAttributes = (transaction, parent, left, right, currentAttributes, attributes) => {
+  const negatedAttributes = new Map()
+  // insert format-start items
+  for (const key in attributes) {
+    const val = attributes[key]
+    const currentVal = currentAttributes.get(key) || null
+    if (!equalAttrs(currentVal, val)) {
+      // save negated attribute (set null if currentVal undefined)
+      negatedAttributes.set(key, currentVal)
+      left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentFormat(key, val))
+      left.integrate(transaction)
+    }
+  }
+  return new ItemInsertionResult(left, right, negatedAttributes)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} currentAttributes
+ * @param {string|object} text
+ * @param {Object<string,any>} attributes
+ * @return {ItemListPosition}
+ *
+ * @private
+ * @function
+ **/
+const insertText = (transaction, parent, left, right, currentAttributes, text, attributes) => {
+  for (const [key] of currentAttributes) {
+    if (attributes[key] === undefined) {
+      attributes[key] = null
+    }
+  }
+  const minPos = minimizeAttributeChanges(left, right, currentAttributes, attributes)
+  const insertPos = insertAttributes(transaction, parent, minPos.left, minPos.right, currentAttributes, attributes)
+  left = insertPos.left
+  right = insertPos.right
+  // insert content
+  const content = text.constructor === String ? new ContentString(/** @type {string} */ (text)) : new ContentEmbed(text)
+  left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, content)
+  left.integrate(transaction)
+  return insertNegatedAttributes(transaction, parent, left, insertPos.right, insertPos.negatedAttributes)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} currentAttributes
+ * @param {number} length
+ * @param {Object<string,any>} attributes
+ * @return {ItemListPosition}
+ *
+ * @private
+ * @function
+ */
+const formatText = (transaction, parent, left, right, currentAttributes, length, attributes) => {
+  const minPos = minimizeAttributeChanges(left, right, currentAttributes, attributes)
+  const insertPos = insertAttributes(transaction, parent, minPos.left, minPos.right, currentAttributes, attributes)
+  const negatedAttributes = insertPos.negatedAttributes
+  left = insertPos.left
+  right = insertPos.right
+  // iterate until first non-format or null is found
+  // delete all formats with attributes[format.key] != null
+  while (length > 0 && right !== null) {
+    if (!right.deleted) {
+      switch (right.content.constructor) {
+        case ContentFormat: {
+          const { key, value } = /** @type {ContentFormat} */ (right.content)
+          const attr = attributes[key]
+          if (attr !== undefined) {
+            if (equalAttrs(attr, value)) {
+              negatedAttributes.delete(key)
+            } else {
+              negatedAttributes.set(key, value)
+            }
+            right.delete(transaction)
+          }
+          updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (right.content))
+          break
+        }
+        case ContentEmbed:
+        case ContentString:
+          if (length < right.length) {
+            getItemCleanStart(transaction, createID(right.id.client, right.id.clock + length))
+          }
+          length -= right.length
+          break
+      }
+    }
+    left = right
+    right = right.right
+  }
+  // Quill just assumes that the editor starts with a newline and that it always
+  // ends with a newline. We only insert that newline when a new newline is
+  // inserted - i.e when length is bigger than type.length
+  if (length > 0) {
+    let newlines = ''
+    for (; length > 0; length--) {
+      newlines += '\n'
+    }
+    left = new Item(nextID(transaction), left, left === null ? null : left.lastId, right, right === null ? null : right.id, parent, null, new ContentString(newlines))
+    left.integrate(transaction)
+  }
+  return insertNegatedAttributes(transaction, parent, left, right, negatedAttributes)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {Item|null} left
+ * @param {Item|null} right
+ * @param {Map<string,any>} currentAttributes
+ * @param {number} length
+ * @return {ItemListPosition}
+ *
+ * @private
+ * @function
+ */
+const deleteText = (transaction, left, right, currentAttributes, length) => {
+  while (length > 0 && right !== null) {
+    if (right.deleted === false) {
+      switch (right.content.constructor) {
+        case ContentFormat:
+          updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (right.content))
+          break
+        case ContentEmbed:
+        case ContentString:
+          if (length < right.length) {
+            getItemCleanStart(transaction, createID(right.id.client, right.id.clock + length))
+          }
+          length -= right.length
+          right.delete(transaction)
+          break
+      }
+    }
+    left = right
+    right = right.right
+  }
+  return { left, right }
+}
+
+/**
+ * The Quill Delta format represents changes on a text document with
+ * formatting information. For mor information visit {@link https://quilljs.com/docs/delta/|Quill Delta}
+ *
+ * @example
+ *   {
+ *     ops: [
+ *       { insert: 'Gandalf', attributes: { bold: true } },
+ *       { insert: ' the ' },
+ *       { insert: 'Grey', attributes: { color: '#cccccc' } }
+ *     ]
+ *   }
+ *
+ */
+
+/**
+  * Attributes that can be assigned to a selection of text.
+  *
+  * @example
+  *   {
+  *     bold: true,
+  *     font-size: '40px'
+  *   }
+  *
+  * @typedef {Object} TextAttributes
+  */
+
+/**
+ * @typedef {Object} DeltaItem
+ * @property {number|undefined} DeltaItem.delete
+ * @property {number|undefined} DeltaItem.retain
+ * @property {string|undefined} DeltaItem.string
+ * @property {Object<string,any>} DeltaItem.attributes
+ */
+
+/**
+ * Event that describes the changes on a YText type.
+ */
+export class YTextEvent extends YEvent {
+  /**
+   * @param {YText} ytext
+   * @param {Transaction} transaction
+   */
+  constructor (ytext, transaction) {
+    super(ytext, transaction)
+    /**
+     * @type {Array<DeltaItem>|null}
+     */
+    this._delta = null
+  }
+
+  /**
+   * Compute the changes in the delta format.
+   * A {@link https://quilljs.com/docs/delta/|Quill Delta}) that represents the changes on the document.
+   *
+   * @type {Array<DeltaItem>}
+   *
+   * @public
+   */
+  get delta () {
+    if (this._delta === null) {
+      const y = /** @type {Doc} */ (this.target.doc)
+      this._delta = []
+      transact(y, transaction => {
+        const delta = /** @type {Array<DeltaItem>} */ (this._delta)
+        const currentAttributes = new Map() // saves all current attributes for insert
+        const oldAttributes = new Map()
+        let item = this.target._start
+        /**
+         * @type {string?}
+         */
+        let action = null
+        /**
+         * @type {Object<string,any>}
+         */
+        const attributes = {} // counts added or removed new attributes for retain
+        /**
+         * @type {string|object}
+         */
+        let insert = ''
+        let retain = 0
+        let deleteLen = 0
+        const addOp = () => {
+          if (action !== null) {
+            /**
+             * @type {any}
+             */
+            let op
+            switch (action) {
+              case 'delete':
+                op = { delete: deleteLen }
+                deleteLen = 0
+                break
+              case 'insert':
+                op = { insert }
+                if (currentAttributes.size > 0) {
+                  op.attributes = {}
+                  for (const [key, value] of currentAttributes) {
+                    if (value !== null) {
+                      op.attributes[key] = value
+                    }
+                  }
+                }
+                insert = ''
+                break
+              case 'retain':
+                op = { retain }
+                if (Object.keys(attributes).length > 0) {
+                  op.attributes = {}
+                  for (const key in attributes) {
+                    op.attributes[key] = attributes[key]
+                  }
+                }
+                retain = 0
+                break
+            }
+            delta.push(op)
+            action = null
+          }
+        }
+        while (item !== null) {
+          switch (item.content.constructor) {
+            case ContentEmbed:
+              if (this.adds(item)) {
+                if (!this.deletes(item)) {
+                  addOp()
+                  action = 'insert'
+                  insert = /** @type {ContentEmbed} */ (item.content).embed
+                  addOp()
+                }
+              } else if (this.deletes(item)) {
+                if (action !== 'delete') {
+                  addOp()
+                  action = 'delete'
+                }
+                deleteLen += 1
+              } else if (!item.deleted) {
+                if (action !== 'retain') {
+                  addOp()
+                  action = 'retain'
+                }
+                retain += 1
+              }
+              break
+            case ContentString:
+              if (this.adds(item)) {
+                if (!this.deletes(item)) {
+                  if (action !== 'insert') {
+                    addOp()
+                    action = 'insert'
+                  }
+                  insert += /** @type {ContentString} */ (item.content).str
+                }
+              } else if (this.deletes(item)) {
+                if (action !== 'delete') {
+                  addOp()
+                  action = 'delete'
+                }
+                deleteLen += item.length
+              } else if (!item.deleted) {
+                if (action !== 'retain') {
+                  addOp()
+                  action = 'retain'
+                }
+                retain += item.length
+              }
+              break
+            case ContentFormat: {
+              const { key, value } = /** @type {ContentFormat} */ (item.content)
+              if (this.adds(item)) {
+                if (!this.deletes(item)) {
+                  const curVal = currentAttributes.get(key) || null
+                  if (!equalAttrs(curVal, value)) {
+                    if (action === 'retain') {
+                      addOp()
+                    }
+                    if (equalAttrs(value, (oldAttributes.get(key) || null))) {
+                      delete attributes[key]
+                    } else {
+                      attributes[key] = value
+                    }
+                  } else {
+                    item.delete(transaction)
+                  }
+                }
+              } else if (this.deletes(item)) {
+                oldAttributes.set(key, value)
+                const curVal = currentAttributes.get(key) || null
+                if (!equalAttrs(curVal, value)) {
+                  if (action === 'retain') {
+                    addOp()
+                  }
+                  attributes[key] = curVal
+                }
+              } else if (!item.deleted) {
+                oldAttributes.set(key, value)
+                const attr = attributes[key]
+                if (attr !== undefined) {
+                  if (!equalAttrs(attr, value)) {
+                    if (action === 'retain') {
+                      addOp()
+                    }
+                    if (value === null) {
+                      attributes[key] = value
+                    } else {
+                      delete attributes[key]
+                    }
+                  } else {
+                    item.delete(transaction)
+                  }
+                }
+              }
+              if (!item.deleted) {
+                if (action === 'insert') {
+                  addOp()
+                }
+                updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (item.content))
+              }
+              break
+            }
+          }
+          item = item.right
+        }
+        addOp()
+        while (delta.length > 0) {
+          const lastOp = delta[delta.length - 1]
+          if (lastOp.retain !== undefined && lastOp.attributes === undefined) {
+            // retain delta's if they don't assign attributes
+            delta.pop()
+          } else {
+            break
+          }
+        }
+      })
+    }
+    return this._delta
+  }
+}
+
+/**
+ * Type that represents text with formatting information.
+ *
+ * This type replaces y-richtext as this implementation is able to handle
+ * block formats (format information on a paragraph), embeds (complex elements
+ * like pictures and videos), and text formats (**bold**, *italic*).
+ *
+ * @extends AbstractType<YTextEvent>
+ */
+export class YText extends AbstractType {
+  /**
+   * @param {String} [string] The initial value of the YText.
+   */
+  constructor (string) {
+    super()
+    /**
+     * Array of pending operations on this type
+     * @type {Array<function():void>?}
+     */
+    this._pending = string !== undefined ? [() => this.insert(0, string)] : []
+  }
+
+  /**
+   * Number of characters of this text type.
+   *
+   * @type {number}
+   */
+  get length () {
+    return this._length
+  }
+
+  /**
+   * @param {Doc} y
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    try {
+      /** @type {Array<function>} */ (this._pending).forEach(f => f())
+    } catch (e) {
+      console.error(e)
+    }
+    this._pending = null
+  }
+
+  _copy () {
+    return new YText()
+  }
+
+  /**
+   * Creates YTextEvent 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 YTextEvent(this, transaction))
+  }
+
+  /**
+   * Returns the unformatted string representation of this YText type.
+   *
+   * @public
+   */
+  toString () {
+    let str = ''
+    /**
+     * @type {Item|null}
+     */
+    let n = this._start
+    while (n !== null) {
+      if (!n.deleted && n.countable && n.content.constructor === ContentString) {
+        str += /** @type {ContentString} */ (n.content).str
+      }
+      n = n.right
+    }
+    return str
+  }
+
+  /**
+   * Returns the unformatted string representation of this YText type.
+   *
+   * @return {string}
+   * @public
+   */
+  toJSON () {
+    return this.toString()
+  }
+
+  /**
+   * Apply a {@link Delta} on this shared YText type.
+   *
+   * @param {any} delta The changes to apply on this element.
+   *
+   * @public
+   */
+  applyDelta (delta) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        /**
+         * @type {ItemListPosition}
+         */
+        let pos = new ItemListPosition(null, this._start)
+        const currentAttributes = new Map()
+        for (let i = 0; i < delta.length; i++) {
+          const op = delta[i]
+          if (op.insert !== undefined) {
+            // Quill assumes that the content starts with an empty paragraph.
+            // Yjs/Y.Text assumes that it starts empty. We always hide that
+            // there is a newline at the end of the content.
+            // If we omit this step, clients will see a different number of
+            // paragraphs, but nothing bad will happen.
+            const ins = (typeof op.insert === 'string' && i === delta.length - 1 && pos.right === null && op.insert.slice(-1) === '\n') ? op.insert.slice(0, -1) : op.insert
+            if (typeof ins !== 'string' || ins.length > 0) {
+              pos = insertText(transaction, this, pos.left, pos.right, currentAttributes, ins, op.attributes || {})
+            }
+          } else if (op.retain !== undefined) {
+            pos = formatText(transaction, this, pos.left, pos.right, currentAttributes, op.retain, op.attributes || {})
+          } else if (op.delete !== undefined) {
+            pos = deleteText(transaction, pos.left, pos.right, currentAttributes, op.delete)
+          }
+        }
+      })
+    } else {
+      /** @type {Array<function>} */ (this._pending).push(() => this.applyDelta(delta))
+    }
+  }
+
+  /**
+   * Returns the Delta representation of this YText type.
+   *
+   * @param {Snapshot} [snapshot]
+   * @param {Snapshot} [prevSnapshot]
+   * @param {function('removed' | 'added', ID):any} [computeYChange]
+   * @return {any} The Delta representation of this type.
+   *
+   * @public
+   */
+  toDelta (snapshot, prevSnapshot, computeYChange) {
+    /**
+     * @type{Array<any>}
+     */
+    const ops = []
+    const currentAttributes = new Map()
+    const doc = /** @type {Doc} */ (this.doc)
+    let str = ''
+    let n = this._start
+    function packStr () {
+      if (str.length > 0) {
+        // pack str with attributes to ops
+        /**
+         * @type {Object<string,any>}
+         */
+        const attributes = {}
+        let addAttributes = false
+        for (const [key, value] of currentAttributes) {
+          addAttributes = true
+          attributes[key] = value
+        }
+        /**
+         * @type {Object<string,any>}
+         */
+        const op = { insert: str }
+        if (addAttributes) {
+          op.attributes = attributes
+        }
+        ops.push(op)
+        str = ''
+      }
+    }
+    // snapshots are merged again after the transaction, so we need to keep the
+    // transalive until we are done
+    transact(doc, transaction => {
+      if (snapshot) {
+        splitSnapshotAffectedStructs(transaction, snapshot)
+      }
+      if (prevSnapshot) {
+        splitSnapshotAffectedStructs(transaction, prevSnapshot)
+      }
+      while (n !== null) {
+        if (isVisible(n, snapshot) || (prevSnapshot !== undefined && isVisible(n, prevSnapshot))) {
+          switch (n.content.constructor) {
+            case ContentString: {
+              const cur = currentAttributes.get('ychange')
+              if (snapshot !== undefined && !isVisible(n, snapshot)) {
+                if (cur === undefined || cur.user !== n.id.client || cur.state !== 'removed') {
+                  packStr()
+                  currentAttributes.set('ychange', computeYChange ? computeYChange('removed', n.id) : { type: 'removed' })
+                }
+              } else if (prevSnapshot !== undefined && !isVisible(n, prevSnapshot)) {
+                if (cur === undefined || cur.user !== n.id.client || cur.state !== 'added') {
+                  packStr()
+                  currentAttributes.set('ychange', computeYChange ? computeYChange('added', n.id) : { type: 'added' })
+                }
+              } else if (cur !== undefined) {
+                packStr()
+                currentAttributes.delete('ychange')
+              }
+              str += /** @type {ContentString} */ (n.content).str
+              break
+            }
+            case ContentEmbed: {
+              packStr()
+              /**
+               * @type {Object<string,any>}
+               */
+              const op = {
+                insert: /** @type {ContentEmbed} */ (n.content).embed
+              }
+              if (currentAttributes.size > 0) {
+                const attrs = /** @type {Object<string,any>} */ ({})
+                op.attributes = attrs
+                for (const [key, value] of currentAttributes) {
+                  attrs[key] = value
+                }
+              }
+              ops.push(op)
+              break
+            }
+            case ContentFormat:
+              if (isVisible(n, snapshot)) {
+                packStr()
+                updateCurrentAttributes(currentAttributes, /** @type {ContentFormat} */ (n.content))
+              }
+              break
+          }
+        }
+        n = n.right
+      }
+      packStr()
+    }, splitSnapshotAffectedStructs)
+    return ops
+  }
+
+  /**
+   * Insert text at a given index.
+   *
+   * @param {number} index The index at which to start inserting.
+   * @param {String} text The text to insert at the specified position.
+   * @param {TextAttributes} [attributes] Optionally define some formatting
+   *                                    information to apply on the inserted
+   *                                    Text.
+   * @public
+   */
+  insert (index, text, attributes) {
+    if (text.length <= 0) {
+      return
+    }
+    const y = this.doc
+    if (y !== null) {
+      transact(y, transaction => {
+        const { left, right, currentAttributes } = findPosition(transaction, this, index)
+        if (!attributes) {
+          attributes = {}
+          // @ts-ignore
+          currentAttributes.forEach((v, k) => { attributes[k] = v })
+        }
+        insertText(transaction, this, left, right, currentAttributes, text, attributes)
+      })
+    } else {
+      /** @type {Array<function>} */ (this._pending).push(() => this.insert(index, text, attributes))
+    }
+  }
+
+  /**
+   * Inserts an embed at a index.
+   *
+   * @param {number} index The index to insert the embed at.
+   * @param {Object} embed The Object that represents the embed.
+   * @param {TextAttributes} attributes Attribute information to apply on the
+   *                                    embed
+   *
+   * @public
+   */
+  insertEmbed (index, embed, attributes = {}) {
+    if (embed.constructor !== Object) {
+      throw new Error('Embed must be an Object')
+    }
+    const y = this.doc
+    if (y !== null) {
+      transact(y, transaction => {
+        const { left, right, currentAttributes } = findPosition(transaction, this, index)
+        insertText(transaction, this, left, right, currentAttributes, embed, attributes)
+      })
+    } else {
+      /** @type {Array<function>} */ (this._pending).push(() => this.insertEmbed(index, embed, attributes))
+    }
+  }
+
+  /**
+   * Deletes text starting from an index.
+   *
+   * @param {number} index Index at which to start deleting.
+   * @param {number} length The number of characters to remove. Defaults to 1.
+   *
+   * @public
+   */
+  delete (index, length) {
+    if (length === 0) {
+      return
+    }
+    const y = this.doc
+    if (y !== null) {
+      transact(y, transaction => {
+        const { left, right, currentAttributes } = findPosition(transaction, this, index)
+        deleteText(transaction, left, right, currentAttributes, length)
+      })
+    } else {
+      /** @type {Array<function>} */ (this._pending).push(() => this.delete(index, length))
+    }
+  }
+
+  /**
+   * Assigns properties to a range of text.
+   *
+   * @param {number} index The position where to start formatting.
+   * @param {number} length The amount of characters to assign properties to.
+   * @param {TextAttributes} attributes Attribute information to apply on the
+   *                                    text.
+   *
+   * @public
+   */
+  format (index, length, attributes) {
+    const y = this.doc
+    if (y !== null) {
+      transact(y, transaction => {
+        const { left, right, currentAttributes } = findPosition(transaction, this, index)
+        if (right === null) {
+          return
+        }
+        formatText(transaction, this, left, right, currentAttributes, length, attributes)
+      })
+    } else {
+      /** @type {Array<function>} */ (this._pending).push(() => this.format(index, length, attributes))
+    }
+  }
+
+  /**
+   * @param {encoding.Encoder} encoder
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YTextRefID)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {YText}
+ *
+ * @private
+ * @function
+ */
+export const readYText = decoder => new YText()
--- a/src/types/YXmlElement.js
+++ b/src/types/YXmlElement.js
@@ -0,0 +1,198 @@
+
+import {
+  YXmlFragment,
+  transact,
+  typeMapDelete,
+  typeMapSet,
+  typeMapGet,
+  typeMapGetAll,
+  typeListForEach,
+  YXmlElementRefID,
+  Snapshot, Doc, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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()
+  }
+
+  /**
+   * 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)
+  }
+
+  /**
+   * 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 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 {encoding.Encoder} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YXmlElementRefID)
+    encoding.writeVarString(encoder, this.nodeName)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {YXmlElement}
+ *
+ * @function
+ */
+export const readYXmlElement = decoder => new YXmlElement(decoding.readVarString(decoder))
--- a/src/types/YXmlEvent.js
+++ b/src/types/YXmlEvent.js
@@ -0,0 +1,39 @@
+
+import {
+  YEvent,
+  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|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|null>}
+     */
+    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 +1,342 @@
+/**
+ * @module YXml
+ */
+
+import {
+  YXmlEvent,
+  YXmlElement,
+  AbstractType,
+  typeListMap,
+  typeListForEach,
+  typeListInsertGenerics,
+  typeListDelete,
+  typeListToArray,
+  YXmlFragmentRefID,
+  callTypeObservers,
+  transact,
+  Doc, ContentType, Transaction, Item, YXmlText, YXmlHook, Snapshot // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+
+/**
+ * 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 {IterableIterator}
+ */
+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 = /** @type {ContentType} */ (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 {ContentType} */ (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 = 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 = []
+  }
+
+  /**
+   * 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()
+  }
+
+  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)
+    }
+  }
+
+  /**
+   * 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)
+  }
+
+  /**
+   * 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 {encoding.Encoder} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YXmlFragmentRefID)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {YXmlFragment}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlFragment = decoder => new YXmlFragment()
--- a/src/types/YXmlHook.js
+++ b/src/types/YXmlHook.js
@@ -0,0 +1,86 @@
+
+import {
+  YMap,
+  YXmlHookRefID
+} from '../internals.js'
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.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)
+  }
+
+  /**
+   * 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 {encoding.Encoder} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    super._write(encoder)
+    encoding.writeVarUint(encoder, YXmlHookRefID)
+    encoding.writeVarString(encoder, this.hookName)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {YXmlHook}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlHook = decoder =>
+  new YXmlHook(decoding.readVarString(decoder))
--- a/src/types/YXmlText.js
+++ b/src/types/YXmlText.js
@@ -0,0 +1,95 @@
+
+import { YText, YXmlTextRefID } from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+
+/**
+ * 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 {
+  _copy () {
+    return new YXmlText()
+  }
+
+  /**
+   * 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 {encoding.Encoder} encoder
+   */
+  _write (encoder) {
+    encoding.writeVarUint(encoder, YXmlTextRefID)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {YXmlText}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlText = decoder => new YXmlText()
--- a/src/utils/DeleteSet.js
+++ b/src/utils/DeleteSet.js
@@ -0,0 +1,313 @@
+
+import {
+  findIndexSS,
+  createID,
+  getState,
+  splitItem,
+  iterateStructs,
+  Item, GC, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+import * as array from 'lib0/array.js'
+import * as math from 'lib0/math.js'
+import * as map from 'lib0/map.js'
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+
+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 += right.len
+      } 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 {ID} id
+ * @param {number} length
+ *
+ * @private
+ * @function
+ */
+export const addToDeleteSet = (ds, id, length) => {
+  map.setIfUndefined(ds.clients, id.client, () => []).push(new DeleteItem(id.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.id.clock === clock + len && 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 {encoding.Encoder} encoder
+ * @param {DeleteSet} ds
+ *
+ * @private
+ * @function
+ */
+export const writeDeleteSet = (encoder, ds) => {
+  encoding.writeVarUint(encoder, ds.clients.size)
+  ds.clients.forEach((dsitems, client) => {
+    encoding.writeVarUint(encoder, client)
+    const len = dsitems.length
+    encoding.writeVarUint(encoder, len)
+    for (let i = 0; i < len; i++) {
+      const item = dsitems[i]
+      encoding.writeVarUint(encoder, item.clock)
+      encoding.writeVarUint(encoder, item.len)
+    }
+  })
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {DeleteSet}
+ *
+ * @private
+ * @function
+ */
+export const readDeleteSet = decoder => {
+  const ds = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder)
+  for (let i = 0; i < numClients; i++) {
+    const client = decoding.readVarUint(decoder)
+    const numberOfDeletes = decoding.readVarUint(decoder)
+    for (let i = 0; i < numberOfDeletes; i++) {
+      addToDeleteSet(ds, createID(client, decoding.readVarUint(decoder)), decoding.readVarUint(decoder))
+    }
+  }
+  return ds
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ *
+ * @private
+ * @function
+ */
+export const readAndApplyDeleteSet = (decoder, transaction, store) => {
+  const unappliedDS = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder)
+  for (let i = 0; i < numClients; i++) {
+    const client = decoding.readVarUint(decoder)
+    const numberOfDeletes = decoding.readVarUint(decoder)
+    const structs = store.clients.get(client) || []
+    const state = getState(store, client)
+    for (let i = 0; i < numberOfDeletes; i++) {
+      const clock = decoding.readVarUint(decoder)
+      const len = decoding.readVarUint(decoder)
+      if (clock < state) {
+        if (state < clock + len) {
+          addToDeleteSet(unappliedDS, createID(client, state), clock + len - 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 < clock + len) {
+            if (!struct.deleted) {
+              if (clock + len < struct.id.clock + struct.length) {
+                structs.splice(index, 0, splitItem(transaction, struct, clock + len - struct.id.clock))
+              }
+              struct.delete(transaction)
+            }
+          } else {
+            break
+          }
+        }
+      } else {
+        addToDeleteSet(unappliedDS, createID(client, clock), len)
+      }
+    }
+  }
+  if (unappliedDS.clients.size > 0) {
+    // TODO: no need for encoding+decoding ds anymore
+    const unappliedDSEncoder = encoding.createEncoder()
+    writeDeleteSet(unappliedDSEncoder, unappliedDS)
+    store.pendingDeleteReaders.push(decoding.createDecoder(encoding.toUint8Array(unappliedDSEncoder)))
+  }
+}
--- a/src/utils/Doc.js
+++ b/src/utils/Doc.js
@@ -0,0 +1,195 @@
+/**
+ * @module Y
+ */
+
+import {
+  StructStore,
+  AbstractType,
+  YArray,
+  YText,
+  YMap,
+  YXmlFragment,
+  transact,
+  Item, Transaction, YEvent // eslint-disable-line
+} from '../internals.js'
+
+import { Observable } from 'lib0/observable.js'
+import * as random from 'lib0/random.js'
+import * as map from 'lib0/map.js'
+
+export const generateNewClientId = random.uint32
+
+/**
+ * A Yjs instance handles the state of shared data.
+ * @extends Observable<string>
+ */
+export class Doc extends Observable {
+  /**
+   * @param {Object} conf configuration
+   * @param {boolean} [conf.gc] Disable garbage collection (default: gc=true)
+   * @param {function(Item):boolean} [conf.gcFilter] Will be called before an Item is garbage collected. Return false to keep the Item.
+   */
+  constructor ({ gc = true, gcFilter = () => true } = {}) {
+    super()
+    this.gc = gc
+    this.gcFilter = gcFilter
+    this.clientID = generateNewClientId()
+    /**
+     * @type {Map<string, AbstractType<YEvent>>}
+     */
+    this.share = new Map()
+    this.store = new StructStore()
+    /**
+     * @type {Transaction | null}
+     */
+    this._transaction = null
+    /**
+     * @type {Array<Transaction>}
+     */
+    this._transactionCleanups = []
+  }
+
+  /**
+   * 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)
+  }
+
+  /**
+   * @param {string} name
+   * @return {YMap<any>}
+   *
+   * @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)
+  }
+
+  /**
+   * Emit `destroy` event and unregister all event handlers.
+   */
+  destroy () {
+    this.emit('destroyed', [true])
+    super.destroy()
+  }
+
+  /**
+   * @param {string} eventName
+   * @param {function} 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 +1,82 @@
+import * as f from 'lib0/function.js'
+
+/**
+ * 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) => {
+  eventHandler.l = eventHandler.l.filter(g => f !== g)
+}
+
+/**
+ * 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.js'
+import * as encoding from 'lib0/encoding.js'
+import * as error from 'lib0/error.js'
+
+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) {
+    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,
+  ID, DeleteSet, YArrayEvent, Transaction, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding.js'
+import * as encoding from 'lib0/encoding.js'
+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(decoding.createDecoder(encodedDs))]))
+            }
+          })
+        })
+      })
+      this.dss.set(userDescription, mergeDeleteSets(ds.map(encodedDs => readDeleteSet(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 = encoding.createEncoder()
+          const ds = this.dss.get(userDescription)
+          if (ds) {
+            writeDeleteSet(encoder, ds)
+            user.get('ds').push([encoding.toUint8Array(encoder)])
+          }
+        }
+      }, 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 = encoding.createEncoder()
+          writeDeleteSet(encoder, ds)
+          yds.push([encoding.toUint8Array(encoder)])
+        }
+      })
+    })
+  }
+
+  /**
+   * @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) {
+      if (isDeleted(ds, id)) {
+        return userDescription
+      }
+    }
+    return null
+  }
+}
--- a/src/utils/RelativePosition.js
+++ b/src/utils/RelativePosition.js
@@ -0,0 +1,272 @@
+
+import {
+  createID,
+  writeID,
+  readID,
+  compareIDs,
+  getState,
+  findRootTypeKey,
+  Item,
+  ContentType,
+  followRedone,
+  ID, Doc, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as error from 'lib0/error.js'
+
+/**
+ * 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
+   */
+  constructor (type, tname, item) {
+    /**
+     * @type {ID|null}
+     */
+    this.type = type
+    /**
+     * @type {string|null}
+     */
+    this.tname = tname
+    /**
+     * @type {ID | null}
+     */
+    this.item = item
+  }
+}
+
+/**
+ * @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))
+
+export class AbsolutePosition {
+  /**
+   * @param {AbstractType<any>} type
+   * @param {number} index
+   */
+  constructor (type, index) {
+    /**
+     * @type {AbstractType<any>}
+     */
+    this.type = type
+    /**
+     * @type {number}
+     */
+    this.index = index
+  }
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} index
+ *
+ * @function
+ */
+export const createAbsolutePosition = (type, index) => new AbsolutePosition(type, index)
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {ID|null} item
+ *
+ * @function
+ */
+export const createRelativePosition = (type, item) => {
+  let typeid = null
+  let tname = null
+  if (type._item === null) {
+    tname = findRootTypeKey(type)
+  } else {
+    typeid = type._item.id
+  }
+  return new RelativePosition(typeid, tname, item)
+}
+
+/**
+ * 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.
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const createRelativePositionFromTypeIndex = (type, index) => {
+  let t = type._start
+  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))
+      }
+      index -= t.length
+    }
+    t = t.right
+  }
+  return createRelativePosition(type, null)
+}
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {RelativePosition} rpos
+ *
+ * @function
+ */
+export const writeRelativePosition = (encoder, rpos) => {
+  const { type, tname, item } = 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()
+  }
+  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|null}
+ *
+ * @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)
+    }
+  }
+  return new RelativePosition(type, tname, itemID)
+}
+
+/**
+ * @param {Uint8Array} uint8Array
+ * @return {RelativePosition|null}
+ */
+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
+  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 = right.parent
+    if (type._item === null || !type._item.deleted) {
+      index = right.deleted || !right.countable ? 0 : res.diff
+      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()
+    }
+    index = type._length
+  }
+  return createAbsolutePosition(type, index)
+}
+
+/**
+ * @param {RelativePosition|null} a
+ * @param {RelativePosition|null} b
+ *
+ * @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/src/utils/Snapshot.js
+++ b/src/utils/Snapshot.js
@@ -0,0 +1,138 @@
+
+import {
+  isDeleted,
+  createDeleteSetFromStructStore,
+  getStateVector,
+  getItemCleanStart,
+  createID,
+  iterateDeletedStructs,
+  writeDeleteSet,
+  writeStateVector,
+  readDeleteSet,
+  readStateVector,
+  createDeleteSet,
+  getState,
+  Transaction, Doc, DeleteSet, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map.js'
+import * as set from 'lib0/set.js'
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+
+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) {
+    if (sv2.get(key) !== value) {
+      return false
+    }
+  }
+  for (const [client, dsitems1] of ds1) {
+    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
+ * @return {Uint8Array}
+ */
+export const encodeSnapshot = snapshot => {
+  const encoder = encoding.createEncoder()
+  writeDeleteSet(encoder, snapshot.ds)
+  writeStateVector(encoder, snapshot.sv)
+  return encoding.toUint8Array(encoder)
+}
+
+/**
+ * @param {Uint8Array} buf
+ * @return {Snapshot}
+ */
+export const decodeSnapshot = buf => {
+  const decoder = decoding.createDecoder(buf)
+  return new Snapshot(readDeleteSet(decoder), readStateVector(decoder))
+}
+
+/**
+ * @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)
+  }
+}
--- a/src/utils/StructStore.js
+++ b/src/utils/StructStore.js
@@ -0,0 +1,271 @@
+
+import {
+  GC,
+  splitItem,
+  GCRef, ItemRef, Transaction, ID, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as math from 'lib0/math.js'
+import * as error from 'lib0/error.js'
+import * as decoding from 'lib0/decoding.js' // eslint-disable-line
+
+export class StructStore {
+  constructor () {
+    /**
+     * @type {Map<number,Array<GC|Item>>}
+     */
+    this.clients = new Map()
+    /**
+     * Store incompleted struct reads here
+     * `i` denotes to the next read operation
+     * We could shift the array of refs instead, but shift is incredible
+     * slow in Chrome for arrays with more than 100k elements
+     * @see tryResumePendingStructRefs
+     * @type {Map<number,{i:number,refs:Array<GCRef|ItemRef>}>}
+     */
+    this.pendingClientsStructRefs = new Map()
+    /**
+     * Stack of pending structs waiting for struct dependencies
+     * Maximum length of stack is structReaders.size
+     * @type {Array<GCRef|ItemRef>}
+     */
+    this.pendingStack = []
+    /**
+     * @type {Array<decoding.Decoder>}
+     */
+    this.pendingDeleteReaders = []
+  }
+}
+
+/**
+ * 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<any>} structs
+ * @param {number} clock
+ * @return {number}
+ *
+ * @private
+ * @function
+ */
+export const findIndexSS = (structs, clock) => {
+  let left = 0
+  let right = structs.length - 1
+  while (left <= right) {
+    const midindex = math.floor((left + right) / 2)
+    const mid = structs[midindex]
+    const midclock = mid.id.clock
+    if (midclock <= clock) {
+      if (clock < midclock + mid.length) {
+        return midindex
+      }
+      left = midindex + 1
+    } else {
+      right = midindex - 1
+    }
+  }
+  // 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.
+ *
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {Item}
+ *
+ * @private
+ * @function
+ */
+// @ts-ignore
+export const getItem = (store, id) => find(store, id)
+
+/**
+ * @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 +1,372 @@
+
+import {
+  getState,
+  createID,
+  writeStructsFromTransaction,
+  writeDeleteSet,
+  DeleteSet,
+  sortAndMergeDeleteSet,
+  getStateVector,
+  findIndexSS,
+  callEventHandlerListeners,
+  Item,
+  generateNewClientId,
+  StructStore, ID, AbstractType, AbstractStruct, YEvent, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as map from 'lib0/map.js'
+import * as math from 'lib0/math.js'
+import * as set from 'lib0/set.js'
+import * as logging from 'lib0/logging.js'
+import { callAll } from 'lib0/function.js'
+
+/**
+ * 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 {Set<ID>}
+     */
+    this._mergeStructs = new Set()
+    /**
+     * @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
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ */
+export const computeUpdateMessageFromTransaction = transaction => {
+  if (transaction.deleteSet.clients.size === 0 && !map.any(transaction.afterState, (clock, client) => transaction.beforeState.get(client) !== clock)) {
+    return null
+  }
+  const encoder = encoding.createEncoder()
+  sortAndMergeDeleteSet(transaction.deleteSet)
+  writeStructsFromTransaction(encoder, transaction)
+  writeDeleteSet(encoder, transaction.deleteSet)
+  return encoder
+}
+
+/**
+ * @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 && right.parent._map.get(right.parentSub) === right) {
+        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) {
+    const structs = /** @type {Array<AbstractStruct>} */ (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
+  for (const [client, deleteItems] of ds.clients) {
+    const structs = /** @type {Array<AbstractStruct>} */ (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
+    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
+                })
+              // 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
+      for (const [client, clock] of transaction.afterState) {
+        const beforeClock = transaction.beforeState.get(client) || 0
+        if (beforeClock !== clock) {
+          const structs = /** @type {Array<AbstractStruct>} */ (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 (const mid of transaction._mergeStructs) {
+        const client = mid.client
+        const clock = mid.clock
+        const structs = /** @type {Array<AbstractStruct>} */ (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 updateMessage = computeUpdateMessageFromTransaction(transaction)
+        if (updateMessage !== null) {
+          doc.emit('update', [encoding.toUint8Array(updateMessage), transaction.origin, doc])
+        }
+      }
+      if (transactionCleanups.length <= i + 1) {
+        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)
+    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 +1,283 @@
+import {
+  mergeDeleteSets,
+  iterateDeletedStructs,
+  keepItem,
+  transact,
+  redoItem,
+  iterateStructs,
+  isParentOf,
+  createID,
+  followRedone,
+  getItemCleanStart,
+  getState,
+  Transaction, Doc, Item, GC, DeleteSet, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as time from 'lib0/time.js'
+import { Observable } from 'lib0/observable.js'
+
+class StackItem {
+  /**
+   * @param {DeleteSet} ds
+   * @param {number} start clock start of the local client
+   * @param {number} len
+   */
+  constructor (ds, start, len) {
+    this.ds = ds
+    this.start = start
+    this.len = len
+    /**
+     * 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
+  const doc = undoManager.doc
+  const scope = undoManager.scope
+  transact(doc, transaction => {
+    while (stack.length > 0 && result === null) {
+      const store = doc.store
+      const clientID = doc.clientID
+      const stackItem = /** @type {StackItem} */ (stack.pop())
+      const stackStartClock = stackItem.start
+      const stackEndClock = stackItem.start + stackItem.len
+      const itemsToRedo = new Set()
+      // @todo iterateStructs should not need the structs parameter
+      const structs = /** @type {Array<GC|Item>} */ (store.clients.get(clientID))
+      let performedChange = false
+      if (stackStartClock !== stackEndClock) {
+        // make sure structs don't overlap with the range of created operations [stackItem.start, stackItem.start + stackItem.end)
+        getItemCleanStart(transaction, createID(clientID, stackStartClock))
+        if (stackEndClock < getState(doc.store, clientID)) {
+          getItemCleanStart(transaction, createID(clientID, stackEndClock))
+        }
+      }
+      iterateDeletedStructs(transaction, stackItem.ds, struct => {
+        if (
+          struct instanceof Item &&
+          scope.some(type => isParentOf(type, struct)) &&
+          // Never redo structs in [stackItem.start, stackItem.start + stackItem.end) because they were created and deleted in the same capture interval.
+          !(struct.id.client === clientID && struct.id.clock >= stackStartClock && struct.id.clock < stackEndClock)
+        ) {
+          itemsToRedo.add(struct)
+        }
+      })
+      itemsToRedo.forEach(struct => {
+        performedChange = redoItem(transaction, struct, itemsToRedo) !== null || performedChange
+      })
+      /**
+       * @type {Array<Item>}
+       */
+      const itemsToDelete = []
+      iterateStructs(transaction, structs, stackStartClock, stackItem.len, 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))
+            }
+            if (item.length > stackItem.len) {
+              getItemCleanStart(transaction, createID(item.id.client, stackEndClock))
+            }
+            struct = item
+          }
+          if (!struct.deleted && scope.some(type => isParentOf(type, /** @type {Item} */ (struct)))) {
+            itemsToDelete.push(struct)
+          }
+        }
+      })
+      // 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 = stackItem
+      if (result != null) {
+        undoManager.emit('stack-item-popped', [{ stackItem: result, type: eventType }, undoManager])
+      }
+    }
+  }, 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, deleteFilter = () => true, trackedOrigins = new Set([null]) } = {}) {
+    if (captureTimeout == null) {
+      captureTimeout = 500
+    }
+    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 beforeState = transaction.beforeState.get(this.doc.clientID) || 0
+      const afterState = transaction.afterState.get(this.doc.clientID) || 0
+      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.ds = mergeDeleteSets([lastOp.ds, transaction.deleteSet])
+        lastOp.len = afterState - lastOp.start
+      } else {
+        // create a new stack op
+        stack.push(new StackItem(transaction.deleteSet, beforeState, afterState - beforeState))
+      }
+      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' }, this])
+    })
+  }
+
+  clear () {
+    this.doc.transact(transaction => {
+      /**
+       * @param {StackItem} stackItem
+       */
+      const clearItem = stackItem => {
+        iterateDeletedStructs(transaction, stackItem.ds, 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/YEvent.js
+++ b/src/utils/YEvent.js
@@ -0,0 +1,226 @@
+
+import {
+  isDeleted,
+  Item, AbstractType, Transaction, AbstractStruct // eslint-disable-line
+} from '../internals.js'
+
+import * as set from 'lib0/set.js'
+import * as array from 'lib0/array.js'
+
+/**
+ * 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
+  }
+
+  /**
+   * Computes the path from `y` to the changed type.
+   *
+   * 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)
+  }
+
+  /**
+   * 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)
+  }
+
+  /**
+   * @return {{added:Set<Item>,deleted:Set<Item>,delta:Array<{insert:Array<any>}|{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 = []
+      /**
+       * @type {Map<string,{ action: 'add' | 'update' | 'delete', oldValue: any}>}
+       */
+      const keys = new Map()
+      changes = {
+        added, deleted, delta, 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()
+        }
+      }
+      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._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 = child._item.parent._start
+      while (c !== child._item && c !== null) {
+        if (!c.deleted) {
+          i++
+        }
+        c = c.right
+      }
+      path.unshift(i)
+    }
+    child = child._item.parent
+  }
+  return path
+}
--- a/src/utils/encoding.js
+++ b/src/utils/encoding.js
@@ -0,0 +1,423 @@
+
+/**
+ * @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,
+  GCRef,
+  ItemRef,
+  writeID,
+  createID,
+  readID,
+  getState,
+  getStateVector,
+  readAndApplyDeleteSet,
+  writeDeleteSet,
+  createDeleteSetFromStructStore,
+  transact,
+  Doc, Transaction, AbstractStruct, StructStore, ID // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as binary from 'lib0/binary.js'
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {Array<AbstractStruct>} 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
+  const startNewStructs = findIndexSS(structs, clock)
+  // write # encoded structs
+  encoding.writeVarUint(encoder, structs.length - startNewStructs)
+  writeID(encoder, createID(client, clock))
+  const firstStruct = structs[startNewStructs]
+  // write first struct with an offset
+  firstStruct.write(encoder, clock - firstStruct.id.clock, 0)
+  for (let i = startNewStructs + 1; i < structs.length; i++) {
+    structs[i].write(encoder, 0, 0)
+  }
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @param {number} numOfStructs
+ * @param {ID} nextID
+ * @return {Array<GCRef|ItemRef>}
+ *
+ * @private
+ * @function
+ */
+const readStructRefs = (decoder, numOfStructs, nextID) => {
+  /**
+   * @type {Array<GCRef|ItemRef>}
+   */
+  const refs = []
+  for (let i = 0; i < numOfStructs; i++) {
+    const info = decoding.readUint8(decoder)
+    const ref = (binary.BITS5 & info) === 0 ? new GCRef(decoder, nextID, info) : new ItemRef(decoder, nextID, info)
+    nextID = createID(nextID.client, nextID.clock + ref.length)
+    refs.push(ref)
+  }
+  return refs
+}
+
+/**
+ * @param {encoding.Encoder} 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, sm.size)
+  sm.forEach((clock, client) => {
+    // @ts-ignore
+    writeStructs(encoder, store.clients.get(client), client, clock)
+  })
+}
+
+/**
+ * @param {decoding.Decoder} decoder The decoder object to read data from.
+ * @return {Map<number,Array<GCRef|ItemRef>>}
+ *
+ * @private
+ * @function
+ */
+export const readClientsStructRefs = decoder => {
+  /**
+   * @type {Map<number,Array<GCRef|ItemRef>>}
+   */
+  const clientRefs = new Map()
+  const numOfStateUpdates = decoding.readVarUint(decoder)
+  for (let i = 0; i < numOfStateUpdates; i++) {
+    const numberOfStructs = decoding.readVarUint(decoder)
+    const nextID = readID(decoder)
+    const refs = readStructRefs(decoder, numberOfStructs, nextID)
+    clientRefs.set(nextID.client, refs)
+  }
+  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
+ *
+ * @private
+ * @function
+ */
+const resumeStructIntegration = (transaction, store) => {
+  const stack = store.pendingStack
+  const clientsStructRefs = store.pendingClientsStructRefs
+  // iterate over all struct readers until we are done
+  while (stack.length !== 0 || clientsStructRefs.size !== 0) {
+    if (stack.length === 0) {
+      // take any first struct from clientsStructRefs and put it on the stack
+      const [client, structRefs] = clientsStructRefs.entries().next().value
+      stack.push(structRefs.refs[structRefs.i++])
+      if (structRefs.refs.length === structRefs.i) {
+        clientsStructRefs.delete(client)
+      }
+    }
+    const ref = stack[stack.length - 1]
+    const m = ref._missing
+    const client = ref.id.client
+    const localClock = getState(store, client)
+    const offset = ref.id.clock < localClock ? localClock - ref.id.clock : 0
+    if (ref.id.clock + offset !== localClock) {
+      // A previous message from this client is missing
+      // check if there is a pending structRef with a smaller clock and switch them
+      const structRefs = clientsStructRefs.get(client)
+      if (structRefs !== undefined) {
+        const r = structRefs.refs[structRefs.i]
+        if (r.id.clock < ref.id.clock) {
+          // put ref with smaller clock on stack instead and continue
+          structRefs.refs[structRefs.i] = ref
+          stack[stack.length - 1] = r
+          // sort the set because this approach might bring the list out of order
+          structRefs.refs = structRefs.refs.slice(structRefs.i).sort((r1, r2) => r1.id.clock - r2.id.clock)
+          structRefs.i = 0
+          continue
+        }
+      }
+      // wait until missing struct is available
+      return
+    }
+    while (m.length > 0) {
+      const missing = m[m.length - 1]
+      if (getState(store, missing.client) <= missing.clock) {
+        const client = missing.client
+        // get the struct reader that has the missing struct
+        const structRefs = clientsStructRefs.get(client)
+        if (structRefs === undefined) {
+          // This update message causally depends on another update message.
+          return
+        }
+        stack.push(structRefs.refs[structRefs.i++])
+        if (structRefs.i === structRefs.refs.length) {
+          clientsStructRefs.delete(client)
+        }
+        break
+      }
+      ref._missing.pop()
+    }
+    if (m.length === 0) {
+      if (offset < ref.length) {
+        ref.toStruct(transaction, store, offset).integrate(transaction)
+      }
+      stack.pop()
+    }
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ *
+ * @private
+ * @function
+ */
+export const tryResumePendingDeleteReaders = (transaction, store) => {
+  const pendingReaders = store.pendingDeleteReaders
+  store.pendingDeleteReaders = []
+  for (let i = 0; i < pendingReaders.length; i++) {
+    readAndApplyDeleteSet(pendingReaders[i], transaction, store)
+  }
+}
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {Transaction} transaction
+ *
+ * @private
+ * @function
+ */
+export const writeStructsFromTransaction = (encoder, transaction) => writeClientsStructs(encoder, transaction.doc.store, transaction.beforeState)
+
+/**
+ * @param {StructStore} store
+ * @param {Map<number, Array<GCRef|ItemRef>>} clientsStructsRefs
+ *
+ * @private
+ * @function
+ */
+const mergeReadStructsIntoPendingReads = (store, clientsStructsRefs) => {
+  const pendingClientsStructRefs = store.pendingClientsStructRefs
+  for (const [client, structRefs] of clientsStructsRefs) {
+    const pendingStructRefs = pendingClientsStructRefs.get(client)
+    if (pendingStructRefs === undefined) {
+      pendingClientsStructRefs.set(client, { refs: structRefs, i: 0 })
+    } else {
+      // merge into existing structRefs
+      const merged = pendingStructRefs.i > 0 ? pendingStructRefs.refs.slice(pendingStructRefs.i) : pendingStructRefs.refs
+      for (let i = 0; i < structRefs.length; i++) {
+        merged.push(structRefs[i])
+      }
+      pendingStructRefs.i = 0
+      pendingStructRefs.refs = merged.sort((r1, r2) => r1.id.clock - r2.id.clock)
+    }
+  }
+}
+
+/**
+ * Read the next Item in a Decoder and fill this Item with the read data.
+ *
+ * This is called when data is received from a remote peer.
+ *
+ * @param {decoding.Decoder} decoder The decoder object to read data from.
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ *
+ * @private
+ * @function
+ */
+export const readStructs = (decoder, transaction, store) => {
+  const clientsStructRefs = readClientsStructRefs(decoder)
+  mergeReadStructsIntoPendingReads(store, clientsStructRefs)
+  resumeStructIntegration(transaction, store)
+  tryResumePendingDeleteReaders(transaction, store)
+}
+
+/**
+ * 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) =>
+  transact(ydoc, transaction => {
+    readStructs(decoder, transaction, ydoc.store)
+    readAndApplyDeleteSet(decoder, transaction, ydoc.store)
+  }, transactionOrigin, false)
+
+/**
+ * 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) =>
+  readUpdate(decoding.createDecoder(update), ydoc, transactionOrigin)
+
+/**
+ * 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 {encoding.Encoder} 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
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateAsUpdate = (doc, encodedTargetStateVector) => {
+  const encoder = encoding.createEncoder()
+  const targetStateVector = encodedTargetStateVector == null ? new Map() : decodeStateVector(encodedTargetStateVector)
+  writeStateAsUpdate(encoder, doc, targetStateVector)
+  return encoding.toUint8Array(encoder)
+}
+
+/**
+ * Read state vector from Decoder and return as Map
+ *
+ * @param {decoding.Decoder} 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)
+  for (let i = 0; i < ssLength; i++) {
+    const client = decoding.readVarUint(decoder)
+    const clock = decoding.readVarUint(decoder)
+    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 decodeStateVector = decodedState => readStateVector(decoding.createDecoder(decodedState))
+
+/**
+ * Write State Vector to `lib0/encoding.js#Encoder`.
+ *
+ * @param {encoding.Encoder} encoder
+ * @param {Map<number,number>} sv
+ * @function
+ */
+export const writeStateVector = (encoder, sv) => {
+  encoding.writeVarUint(encoder, sv.size)
+  sv.forEach((clock, client) => {
+    encoding.writeVarUint(encoder, client)
+    encoding.writeVarUint(encoder, clock)
+  })
+  return encoder
+}
+
+/**
+ * Write State Vector to `lib0/encoding.js#Encoder`.
+ *
+ * @param {encoding.Encoder} encoder
+ * @param {Doc} doc
+ *
+ * @function
+ */
+export const writeDocumentStateVector = (encoder, doc) => writeStateVector(encoder, getStateVector(doc.store))
+
+/**
+ * Encode State as Uint8Array.
+ *
+ * @param {Doc} doc
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateVector = doc => {
+  const encoder = encoding.createEncoder()
+  writeDocumentStateVector(encoder, doc)
+  return encoding.toUint8Array(encoder)
+}
--- 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 = child.parent._item
+  }
+  return false
+}
--- a/src/y.js
+++ b/src/y.js
@@ -1,241 +0,0 @@
-import debug from 'debug'
-import extendConnector from './Connector.js'
-import extendDatabase from './Database.js'
-import extendTransaction from './Transaction.js'
-import extendStruct from './Struct.js'
-import extendUtils from './Utils.js'
-
-extendConnector(Y)
-extendDatabase(Y)
-extendTransaction(Y)
-extendStruct(Y)
-extendUtils(Y)
-
-Y.debug = debug
-
-var requiringModules = {}
-
-Y.requiringModules = requiringModules
-
-Y.extend = function (name, value) {
-  if (arguments.length === 2 && typeof name === 'string') {
-    if (value instanceof Y.utils.CustomTypeDefinition) {
-      Y[name] = value.parseArguments
-    } else {
-      Y[name] = value
-    }
-    if (requiringModules[name] != null) {
-      requiringModules[name].resolve()
-      delete requiringModules[name]
-    }
-  } else {
-    for (var i = 0; i < arguments.length; i++) {
-      var f = arguments[i]
-      if (typeof f === 'function') {
-        f(Y)
-      } else {
-        throw new Error('Expected function!')
-      }
-    }
-  }
-}
-
-Y.requestModules = requestModules
-function requestModules (modules) {
-  var sourceDir
-  if (Y.sourceDir === null) {
-    sourceDir = null
-  } else {
-    sourceDir = Y.sourceDir || '/bower_components'
-  }
-  // determine if this module was compiled for es5 or es6 (y.js vs. y.es6)
-  // if Insert.execute is a Function, then it isnt a generator..
-  // then load the es5(.js) files..
-  var extention = typeof regeneratorRuntime !== 'undefined' ? '.js' : '.es6'
-  var promises = []
-  for (var i = 0; i < modules.length; i++) {
-    var module = modules[i].split('(')[0]
-    var modulename = 'y-' + module.toLowerCase()
-    if (Y[module] == null) {
-      if (requiringModules[module] == null) {
-        // module does not exist
-        if (typeof window !== 'undefined' && window.Y !== 'undefined') {
-          if (sourceDir != null) {
-            var imported = document.createElement('script')
-            imported.src = sourceDir + '/' + modulename + '/' + modulename + extention
-            document.head.appendChild(imported)
-          }
-          let requireModule = {}
-          requiringModules[module] = requireModule
-          requireModule.promise = new Promise(function (resolve) {
-            requireModule.resolve = resolve
-          })
-          promises.push(requireModule.promise)
-        } else {
-          console.info('YJS: Please do not depend on automatic requiring of modules anymore! Extend modules as follows `require(\'y-modulename\')(Y)`')
-          require(modulename)(Y)
-        }
-      } else {
-        promises.push(requiringModules[modules[i]].promise)
-      }
-    }
-  }
-  return Promise.all(promises)
-}
-
-/* ::
-type MemoryOptions = {
-  name: 'memory'
-}
-type IndexedDBOptions = {
-  name: 'indexeddb',
-  namespace: string
-}
-type DbOptions = MemoryOptions | IndexedDBOptions
-
-type WebRTCOptions = {
-  name: 'webrtc',
-  room: string
-}
-type WebsocketsClientOptions = {
-  name: 'websockets-client',
-  room: string
-}
-type ConnectionOptions = WebRTCOptions | WebsocketsClientOptions
-
-type YOptions = {
-  connector: ConnectionOptions,
-  db: DbOptions,
-  types: Array<TypeName>,
-  sourceDir: string,
-  share: {[key: string]: TypeName}
-}
-*/
-
-export default function Y (opts/* :YOptions */) /* :Promise<YConfig> */ {
-  if (opts.hasOwnProperty('sourceDir')) {
-    Y.sourceDir = opts.sourceDir
-  }
-  opts.types = opts.types != null ? opts.types : []
-  var modules = [opts.db.name, opts.connector.name].concat(opts.types)
-  for (var name in opts.share) {
-    modules.push(opts.share[name])
-  }
-  return new Promise(function (resolve, reject) {
-    if (opts == null) reject(new Error('An options object is expected!'))
-    else if (opts.connector == null) reject(new Error('You must specify a connector! (missing connector property)'))
-    else if (opts.connector.name == null) reject(new Error('You must specify connector name! (missing connector.name property)'))
-    else if (opts.db == null) reject(new Error('You must specify a database! (missing db property)'))
-    else if (opts.connector.name == null) reject(new Error('You must specify db name! (missing db.name property)'))
-    else {
-      opts = Y.utils.copyObject(opts)
-      opts.connector = Y.utils.copyObject(opts.connector)
-      opts.db = Y.utils.copyObject(opts.db)
-      opts.share = Y.utils.copyObject(opts.share)
-      Y.requestModules(modules).then(function () {
-        var yconfig = new YConfig(opts)
-        yconfig.db.whenUserIdSet(function () {
-          yconfig.init(function () {
-            resolve(yconfig)
-          })
-        })
-      }).catch(reject)
-    }
-  })
-}
-
-class YConfig extends Y.utils.NamedEventHandler {
-  /* ::
-  db: Y.AbstractDatabase;
-  connector: Y.AbstractConnector;
-  share: {[key: string]: any};
-  options: Object;
-  */
-  constructor (opts, callback) {
-    super()
-    this.options = opts
-    this.db = new Y[opts.db.name](this, opts.db)
-    this.connector = new Y[opts.connector.name](this, opts.connector)
-    this.connected = true
-  }
-  init (callback) {
-    var opts = this.options
-    var share = {}
-    this.share = share
-    this.db.requestTransaction(function * requestTransaction () {
-      // create shared object
-      for (var propertyname in opts.share) {
-        var typeConstructor = opts.share[propertyname].split('(')
-        var typeName = typeConstructor.splice(0, 1)
-        var type = Y[typeName]
-        var typedef = type.typeDefinition
-        var id = ['_', typedef.struct + '_' + typeName + '_' + propertyname + '_' + typeConstructor]
-        var args = []
-        if (typeConstructor.length === 1) {
-          try {
-            args = JSON.parse('[' + typeConstructor[0].split(')')[0] + ']')
-          } catch (e) {
-            throw new Error('Was not able to parse type definition! (share.' + propertyname + ')')
-          }
-          if (type.typeDefinition.parseArguments == null) {
-            throw new Error(typeName + ' does not expect arguments!')
-          } else {
-            args = typedef.parseArguments(args[0])[1]
-          }
-        }
-        share[propertyname] = yield * this.store.initType.call(this, id, args)
-      }
-      this.store.whenTransactionsFinished()
-        .then(callback)
-    })
-  }
-  isConnected () {
-    return this.connector.isSynced
-  }
-  disconnect () {
-    if (this.connected) {
-      this.connected = false
-      return this.connector.disconnect()
-    } else {
-      return Promise.resolve()
-    }
-  }
-  reconnect () {
-    if (!this.connected) {
-      this.connected = true
-      return this.connector.reconnect()
-    } else {
-      return Promise.resolve()
-    }
-  }
-  destroy () {
-    var self = this
-    return this.close().then(function () {
-      if (self.db.deleteDB != null) {
-        return self.db.deleteDB()
-      } else {
-        return Promise.resolve()
-      }
-    }).then(() => {
-      // remove existing event listener
-      super.destroy()
-    })
-  }
-  close () {
-    var self = this
-    this.share = null
-    if (this.connector.destroy != null) {
-      this.connector.destroy()
-    } else {
-      this.connector.disconnect()
-    }
-    return this.db.whenTransactionsFinished().then(function () {
-      self.db.destroyTypes()
-      // make sure to wait for all transactions before destroying the db
-      self.db.requestTransaction(function * () {
-        yield * self.db.destroy()
-      })
-      return self.db.whenTransactionsFinished()
-    })
-  }
-}
--- 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-lib/helper.js
+++ b/tests-lib/helper.js
@@ -1,191 +0,0 @@
-
-import _Y from '../../yjs/src/y.js'
-
-import yMemory from '../../y-memory/src/y-memory.js'
-import yArray from '../../y-array/src/y-array.js'
-import yMap from '../../y-map/src/Map.js'
-import yTest from './test-connector.js'
-
-import Chance from 'chance'
-
-export let Y = _Y
-
-Y.extend(yMemory, yArray, yMap, yTest)
-
-export async function garbageCollectUsers (t, users) {
-  await flushAll(t, users)
-  await Promise.all(users.map(u => u.db.emptyGarbageCollector()))
-}
-
-/*
- * 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
- */
-export async function compareUsers (t, users) {
-  await Promise.all(users.map(u => u.reconnect()))
-  if (users[0].connector.testRoom == null) {
-    await wait(100)
-  }
-  await flushAll(t, users)
-  await wait()
-  await flushAll(t, users)
-
-  var userTypeContents = users.map(u => u.share.array._content.map(c => c.val || JSON.stringify(c.type)))
-
-  await users[0].db.garbageCollect()
-  await users[0].db.garbageCollect()
-
-  // disconnect all except user 0
-  await Promise.all(users.slice(1).map(async u =>
-    u.disconnect()
-  ))
-  if (users[0].connector.testRoom == null) {
-    await wait(100)
-  }
-  // reconnect all
-  await Promise.all(users.map(u => u.reconnect()))
-  if (users[0].connector.testRoom == null) {
-    await wait(100)
-  }
-  await users[0].connector.testRoom.flushAll(users)
-  await Promise.all(users.map(u =>
-    new Promise(function (resolve) {
-      u.connector.whenSynced(resolve)
-    })
-  ))
-  let filterDeletedOps = users.every(u => u.db.gc === false)
-  var data = await Promise.all(users.map(async (u) => {
-    var data = {}
-    u.db.requestTransaction(function * () {
-      var os = yield * this.getOperationsUntransformed()
-      data.os = {}
-      for (let i = 0; i < os.untransformed.length; i++) {
-        let op = os.untransformed[i]
-        op = Y.Struct[op.struct].encode(op)
-        delete op.origin
-        /*
-          If gc = false, it is necessary to filter deleted ops
-          as they might have been split up differently..
-         */
-        if (filterDeletedOps) {
-          let opIsDeleted = yield * this.isDeleted(op.id)
-          if (!opIsDeleted) {
-            data.os[JSON.stringify(op.id)] = op
-          }
-        } else {
-          data.os[JSON.stringify(op.id)] = op
-        }
-      }
-      data.ds = yield * this.getDeleteSet()
-      data.ss = yield * this.getStateSet()
-    })
-    await u.db.whenTransactionsFinished()
-    return data
-  }))
-  for (var i = 0; i < data.length - 1; i++) {
-    await t.asyncGroup(async () => {
-      t.compare(userTypeContents[i], userTypeContents[i + 1], 'types')
-      t.compare(data[i].os, data[i + 1].os, 'os')
-      t.compare(data[i].ds, data[i + 1].ds, 'ds')
-      t.compare(data[i].ss, data[i + 1].ss, 'ss')
-    }, `Compare user${i} with user${i + 1}`)
-  }
-  await Promise.all(users.map(async (u) => {
-    await u.close()
-  }))
-}
-
-export async function initArrays (t, opts) {
-  var result = {
-    users: []
-  }
-  var share = Object.assign({ flushHelper: 'Map', array: 'Array' }, opts.share)
-  var chance = opts.chance || new Chance(t.getSeed() * 1000000000)
-  var connector = Object.assign({ room: 'debugging_' + t.name, testContext: t, chance }, opts.connector)
-  for (let i = 0; i < opts.users; i++) {
-    let dbOpts
-    let connOpts
-    if (i === 0) {
-      // Only one instance can gc!
-      dbOpts = Object.assign({ gc: true }, opts.db)
-      connOpts = Object.assign({ role: 'master' }, connector)
-    } else {
-      dbOpts = Object.assign({ gc: false }, opts.db)
-      connOpts = Object.assign({ role: 'slave' }, connector)
-    }
-    let y = await Y({
-      connector: connOpts,
-      db: dbOpts,
-      share: share
-    })
-    result.users.push(y)
-    for (let name in share) {
-      result[name + i] = y.share[name]
-    }
-  }
-  result.array0.delete(0, result.array0.length)
-  if (result.users[0].connector.testRoom != null) {
-    // flush for sync if test-connector
-    await result.users[0].connector.testRoom.flushAll(result.users)
-  }
-  await Promise.all(result.users.map(u => {
-    return new Promise(function (resolve) {
-      u.connector.whenSynced(resolve)
-    })
-  }))
-  await flushAll(t, result.users)
-  return result
-}
-
-export async function flushAll (t, users) {
-  // users = users.filter(u => u.connector.isSynced)
-  if (users.length === 0) {
-    return
-  }
-  await wait(0)
-  if (users[0].connector.testRoom != null) {
-    // use flushAll method specified in Test Connector
-    await users[0].connector.testRoom.flushAll(users)
-  } else {
-    // flush for any connector
-    await Promise.all(users.map(u => { return u.db.whenTransactionsFinished() }))
-
-    var flushCounter = users[0].share.flushHelper.get('0') || 0
-    flushCounter++
-    await Promise.all(users.map(async (u, i) => {
-      // wait for all users to set the flush counter to the same value
-      await new Promise(resolve => {
-        function observer () {
-          var allUsersReceivedUpdate = true
-          for (var i = 0; i < users.length; i++) {
-            if (u.share.flushHelper.get(i + '') !== flushCounter) {
-              allUsersReceivedUpdate = false
-              break
-            }
-          }
-          if (allUsersReceivedUpdate) {
-            resolve()
-          }
-        }
-        u.share.flushHelper.observe(observer)
-        u.share.flushHelper.set(i + '', flushCounter)
-      })
-    }))
-  }
-}
-
-export async function flushSome (t, users) {
-  if (users[0].connector.testRoom == null) {
-    // if not test-connector, wait for some time for operations to arrive
-    await wait(100)
-  }
-}
-
-export function wait (t) {
-  return new Promise(function (resolve) {
-    setTimeout(resolve, t != null ? t : 100)
-  })
-}
--- a/tests-lib/test-connector.js
+++ b/tests-lib/test-connector.js
@@ -1,156 +0,0 @@
-/* global Y */
-import { wait } from './helper.js'
-
-var rooms = {}
-
-export class TestRoom {
-  constructor (roomname) {
-    this.room = roomname
-    this.users = {}
-    this.nextUserId = 0
-  }
-  join (connector) {
-    if (connector.userId == null) {
-      connector.setUserId('' + (this.nextUserId++))
-    }
-    Object.keys(this.users).forEach(uid => {
-      let user = this.users[uid]
-      if (user.role === 'master' || connector.role === 'master') {
-        this.users[uid].userJoined(connector.userId, connector.role)
-        connector.userJoined(uid, this.users[uid].role)
-      }
-    })
-    this.users[connector.userId] = connector
-  }
-  leave (connector) {
-    delete this.users[connector.userId]
-    Object.keys(this.users).forEach(uid => {
-      this.users[uid].userLeft(connector.userId)
-    })
-  }
-  send (sender, receiver, m) {
-    m = JSON.parse(JSON.stringify(m))
-    var user = this.users[receiver]
-    if (user != null) {
-      user.receiveMessage(sender, m)
-    }
-  }
-  broadcast (sender, m) {
-    Object.keys(this.users).forEach(receiver => {
-      this.send(sender, receiver, m)
-    })
-  }
-  async flushAll (users) {
-    let flushing = true
-    let allUserIds = Object.keys(this.users)
-    if (users == null) {
-      users = allUserIds.map(id => this.users[id].y)
-    }
-    while (flushing) {
-      await wait(10)
-      let res = await Promise.all(allUserIds.map(id => this.users[id]._flushAll(users)))
-      flushing = res.some(status => status === 'flushing')
-    }
-  }
-}
-
-function getTestRoom (roomname) {
-  if (rooms[roomname] == null) {
-    rooms[roomname] = new TestRoom(roomname)
-  }
-  return rooms[roomname]
-}
-
-export default function extendTestConnector (Y) {
-  class TestConnector 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.forwardAppliedOperations = options.role === 'master'
-      super(y, options)
-      this.options = options
-      this.room = options.room
-      this.chance = options.chance
-      this.testRoom = getTestRoom(this.room)
-      this.testRoom.join(this)
-    }
-    disconnect () {
-      this.testRoom.leave(this)
-      return super.disconnect()
-    }
-    reconnect () {
-      this.testRoom.join(this)
-      return super.reconnect()
-    }
-    send (uid, message) {
-      this.testRoom.send(this.userId, uid, message)
-    }
-    broadcast (message) {
-      this.testRoom.broadcast(this.userId, message)
-    }
-    async whenSynced (f) {
-      var synced = false
-      var periodicFlushTillSync = () => {
-        if (synced) {
-          f()
-        } else {
-          this.testRoom.flushAll([this.y]).then(function () {
-            setTimeout(periodicFlushTillSync, 10)
-          })
-        }
-      }
-      periodicFlushTillSync()
-      return super.whenSynced(function () {
-        synced = true
-      })
-    }
-    receiveMessage (sender, m) {
-      if (this.userId !== sender && this.connections[sender] != null) {
-        var buffer = this.connections[sender].buffer
-        if (buffer == null) {
-          buffer = this.connections[sender].buffer = []
-        }
-        buffer.push(m)
-        if (this.chance.bool({likelihood: 30})) {
-          // flush 1/2 with 30% chance
-          var flushLength = Math.round(buffer.length / 2)
-          buffer.splice(0, flushLength).forEach(m => {
-            super.receiveMessage(sender, m)
-          })
-        }
-      }
-    }
-    async _flushAll (flushUsers) {
-      if (flushUsers.some(u => u.connector.userId === this.userId)) {
-        // this one needs to sync with every other user
-        flushUsers = Object.keys(this.connections).map(id => this.testRoom.users[id].y)
-      }
-      var finished = []
-      for (let i = 0; i < flushUsers.length; i++) {
-        let userId = flushUsers[i].connector.userId
-        if (userId !== this.userId && this.connections[userId] != null) {
-          let buffer = this.connections[userId].buffer
-          if (buffer != null) {
-            var messages = buffer.splice(0)
-            for (let j = 0; j < messages.length; j++) {
-              let p = super.receiveMessage(userId, messages[j])
-              finished.push(p)
-            }
-          }
-        }
-      }
-      await Promise.all(finished)
-      await this.y.db.whenTransactionsFinished()
-      return finished.length > 0 ? 'flushing' : 'done'
-    }
-  }
-  Y.extend('test', TestConnector)
-}
-
-if (typeof Y !== 'undefined') {
-  extendTestConnector(Y)
-}
--- a/tests/consistency.tests.js
+++ b/tests/consistency.tests.js
@@ -0,0 +1,19 @@
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing.js'
+
+/**
+ * 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)
+}
--- a/tests/encoding.tests.js
+++ b/tests/encoding.tests.js
@@ -0,0 +1,28 @@
+import * as t from 'lib0/testing.js'
+
+import {
+  contentRefs,
+  readContentBinary,
+  readContentDeleted,
+  readContentString,
+  readContentJSON,
+  readContentEmbed,
+  readContentType,
+  readContentFormat,
+  readContentAny
+} from '../src/internals.js'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testStructReferences = tc => {
+  t.assert(contentRefs.length === 9)
+  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)
+}
--- a/tests/index.js
+++ b/tests/index.js
@@ -0,0 +1,24 @@
+
+import * as array from './y-array.tests.js'
+import * as map from './y-map.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 consistency from './consistency.tests.js'
+
+import { runTests } from 'lib0/testing.js'
+import { isBrowser, isNode } from 'lib0/environment.js'
+import * as log from 'lib0/logging.js'
+
+if (isBrowser) {
+  log.createVConsole(document.body)
+}
+runTests({
+  map, array, text, xml, consistency, encoding, undoredo
+}).then(success => {
+  /* istanbul ignore next */
+  if (isNode) {
+    process.exit(success ? 0 : 1)
+  }
+})
--- a/tests/testHelper.js
+++ b/tests/testHelper.js
@@ -0,0 +1,416 @@
+import * as Y from '../src/index.js'
+
+import {
+  createDeleteSetFromStructStore,
+  getStateVector,
+  Item,
+  DeleteItem, DeleteSet, StructStore, Doc // eslint-disable-line
+} from '../src/internals.js'
+
+import * as t from 'lib0/testing.js'
+import * as prng from 'lib0/prng.js'
+import * as encoding from 'lib0/encoding.js'
+import * as decoding from 'lib0/decoding.js'
+import * as syncProtocol from 'y-protocols/sync.js'
+import * as object from 'lib0/object.js'
+export * from '../src/internals.js'
+
+/**
+ * @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 class TestYInstance extends 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)
+    // set up observe on local model
+    this.on('update', /** @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.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)
+      }
+      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.Array<any>,array1:Y.Array<any>,array2:Y.Array<any>,map0:Y.Map<any>,map1:Y.Map<any>,map2:Y.Map<any>,map3:Y.Map<any>,text0:Y.Text,text1:Y.Text,text2:Y.Text,xml0:Y.XmlElement,xml1:Y.XmlElement,xml2:Y.XmlElement}}
+ */
+export const init = (tc, { users = 5 } = {}, initTestObject) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const result = {
+    users: []
+  }
+  const gen = tc.prng
+  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.get('array', Y.Array)
+    result['map' + i] = y.get('map', Y.Map)
+    result['xml' + i] = y.get('xml', Y.XmlElement)
+    result['text' + i] = y.get('text', Y.Text)
+  }
+  testConnector.syncAll()
+  result.testObjects = result.users.map(initTestObject || (() => null))
+  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()) {}
+  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.XmlElement).toString())
+  const userTextValues = users.map(u => u.getText('text').toDelta())
+  for (const u of users) {
+    t.assert(u.store.pendingDeleteReaders.length === 0)
+    t.assert(u.store.pendingStack.length === 0)
+    t.assert(u.store.pendingClientsStructRefs.size === 0)
+  }
+  // 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])
+    t.compare(getStateVector(users[i].store), getStateVector(users[i + 1].store))
+    compareDS(createDeleteSetFromStructStore(users[i].store), createDeleteSetFromStructStore(users[i + 1].store))
+    compareStructStores(users[i].store, users[i + 1].store)
+  }
+  users.map(u => u.destroy())
+}
+
+/**
+ * @param {Item?} a
+ * @param {Item?} b
+ * @return {boolean}
+ */
+export const compareItemIDs = (a, b) => a === b || (a !== null && b != null && Y.compareIDs(a.id, b.id))
+
+/**
+ * @param {StructStore} ss1
+ * @param {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 ||
+        s1.length !== s2.length
+      ) {
+        t.fail('Structs dont match')
+      }
+      if (s1 instanceof Item) {
+        if (
+          !(s2 instanceof 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 {DeleteSet} ds1
+ * @param {DeleteSet} ds2
+ */
+export const compareDS = (ds1, ds2) => {
+  t.assert(ds1.clients.size === ds2.clients.size)
+  for (const [client, deleteItems1] of ds1.clients) {
+    const deleteItems2 = /** @type {Array<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.int31(gen, 0, 100) <= 2) {
+      // 2% chance to disconnect/reconnect a random user
+      if (prng.bool(gen)) {
+        testConnector.disconnectRandom()
+      } else {
+        testConnector.reconnectRandom()
+      }
+    } else if (prng.int31(gen, 0, 100) <= 1) {
+      // 1% chance to flush all
+      testConnector.flushAllMessages()
+    } else if (prng.int31(gen, 0, 100) <= 50) {
+      // 50% chance to flush a random message
+      testConnector.flushRandomMessage()
+    }
+    const user = prng.int31(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 +1,248 @@
+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.js'
+
+/**
+ * @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' }])
+}
+
+/**
+ * @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)
+    event.stackItem.meta.set('test', counter++)
+  })
+  undoManager.on('stack-item-popped', /** @param {any} event */ event => {
+    t.assert(event.type != null)
+    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)
+}
--- a/tests/y-array.tests.js
+++ b/tests/y-array.tests.js
@@ -0,0 +1,494 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing.js'
+import * as prng from 'lib0/prng.js'
+import * as math from 'lib0/math.js'
+
+/**
+ * @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 => {
+  var { 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 => {
+  var { 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)
+}
+
+/**
+ * @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')
+    var uniqueNumber = getUniqueNumber()
+    var content = []
+    var len = prng.int31(gen, 1, 4)
+    for (var i = 0; i < len; i++) {
+      content.push(uniqueNumber)
+    }
+    var pos = prng.int31(gen, 0, yarray.length)
+    yarray.insert(pos, content)
+  },
+  function insertTypeArray (user, gen) {
+    const yarray = user.getArray('array')
+    var pos = prng.int31(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Array()])
+    var array2 = yarray.get(pos)
+    array2.insert(0, [1, 2, 3, 4])
+  },
+  function insertTypeMap (user, gen) {
+    const yarray = user.getArray('array')
+    var pos = prng.int31(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Map()])
+    var map = yarray.get(pos)
+    map.set('someprop', 42)
+    map.set('someprop', 43)
+    map.set('someprop', 44)
+  },
+  function _delete (user, gen) {
+    const yarray = user.getArray('array')
+    var length = yarray.length
+    if (length > 0) {
+      var somePos = prng.int31(gen, 0, length - 1)
+      var delLength = prng.int31(gen, 1, math.min(2, length - somePos))
+      if (prng.bool(gen)) {
+        var type = yarray.get(somePos)
+        if (type.length > 0) {
+          somePos = prng.int31(gen, 0, type.length - 1)
+          delLength = prng.int31(gen, 0, math.min(2, type.length - somePos))
+          type.delete(somePos, delLength)
+        }
+      } else {
+        yarray.delete(somePos, delLength)
+      }
+    }
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests4 = tc => {
+  applyRandomTests(tc, arrayTransactions, 4)
+}
+
+/**
+ * @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 +1,566 @@
+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.js'
+import * as prng from 'lib0/prng.js'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicMapTests = tc => {
+  const { testConnector, users, map0, map1, map2 } = init(tc, { users: 3 })
+  users[2].disconnect()
+
+  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('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)')
+
+  users[2].connect()
+  testConnector.flushAllMessages()
+
+  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)')
+
+  // compare disconnected user
+  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) {
+    var 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) {
+    var u = user.getMap('map')
+    t.compare(u.get('stuff'), 'c1')
+  }
+  compare(users)
+}
+
+/**
+ * @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) {
+    var u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+  }
+  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) {
+    var 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) {
+    var 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 (var 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 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'])
+    var value = prng.utf16String(gen)
+    user.getMap('map').set(key, value)
+  },
+  function setType (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    var 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, 10)
+}
+
+/**
+ * @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 +1,182 @@
+import * as Y from './testHelper.js'
+import * as t from 'lib0/testing.js'
+const { init, compare } = Y
+
+/**
+ * @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 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 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')
+}
--- a/tests/y-xml.tests.js
+++ b/tests/y-xml.tests.js
@@ -0,0 +1,75 @@
+import { init, compare } from './testHelper.js'
+import * as Y from '../src/index.js'
+
+import * as t from 'lib0/testing.js'
+
+/**
+ * @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 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)
+}
--- 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"]
+}
--- a/y.js
+++ b/y.js
--- a/y.js.map
+++ b/y.js.map
--- a/y.node.js
+++ b/y.node.js
--- a/y.node.js.map
+++ b/y.node.js.map
--- a/Show More
+++ b/Show More