96 changed files with 24752 additions and 5620 deletions
--- a/.github/workflows/node.js.yml
+++ b/.github/workflows/node.js.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: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        node-version: [16.x, 20.x]
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Use Node.js ${{ matrix.node-version }}
+      uses: actions/setup-node@v3
+      with:
+        node-version: ${{ matrix.node-version }}
+    - run: npm ci
+    - run: npm run lint
+    - run: npm run test
+      env:
+        CI: true
--- a/.gitignore
+++ b/.gitignore
@ -1,2 +1,4 @@
 node_modules
-bower_components
+dist
+.vscode
+docs
--- a/.jsdoc.json
+++ b/.jsdoc.json
@ -0,0 +1,52 @@
+{
+  "sourceType": "module",
+  "tags": {
+    "allowUnknownTags": true,
+    "dictionaries": ["jsdoc"]
+  },
+  "source": {
+    "include": ["./src"],
+    "includePattern": ".js$"
+  },
+  "plugins": [
+    "plugins/markdown"
+  ],
+  "templates": {
+    "referenceTitle": "Yjs",
+    "disableSort": false,
+    "useCollapsibles": true,
+    "collapse": true,
+    "resources": {
+      "yjs.dev": "Website",
+      "docs.yjs.dev": "Docs",
+      "discuss.yjs.dev": "Forum",
+      "https://gitter.im/Yjs/community": "Chat"
+    },
+    "logo": {
+      "url": "https://yjs.dev/images/logo/yjs-512x512.png",
+      "width": "162px",
+      "height": "162px",
+      "link": "/"
+    },
+    "tabNames": {
+      "api": "API",
+      "tutorials": "Examples"
+    },
+    "footerText": "Shared Editing",
+    "css": [
+      "./style.css"
+    ],
+    "default": {
+      "staticFiles": {
+          "include": []
+      }
+    }
+  },
+  "opts": {
+    "destination": "./docs/",
+    "encoding": "utf8",
+    "private": false,
+    "recurse": true,
+    "template": "./node_modules/tui-jsdoc-template"
+  }
+}
--- a/.markdownlint.json
+++ b/.markdownlint.json
@ -0,0 +1,4 @@
+{
+  "default": true,
+  "no-inline-html": false
+}
--- a/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.es6"></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
@ -1,25 +0,0 @@
-/* global Y, ace */
-
-// initialize a shared object. This function call returns a promise!
-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/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
@ -1,75 +0,0 @@
-/* @flow */
-/* global Y */
-
-// 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 () {
-    var len
-    while ((len = y.share.chat.length) > 7) {
-      y.share.chat.delete(0)        
-    }
-  }
-  // 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 (var i = 0; i < event.length; i++) {
-        appendMessage(event.values[i], event.index + i)
-      }
-    } else if (event.type === 'delete') {
-      for (var 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.es6"></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
@ -1,69 +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.es6"></script>
-    <script src="../bower_components/y-array/y-array.es6"></script>
-    <script src="../bower_components/y-text/y-text.es6"></script>
-    <script src="../bower_components/y-websockets-client/y-websockets-client.es6"></script>
-    <script src="../bower_components/y-memory/y-memory.es6"></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
@ -1,31 +0,0 @@
-/* global Y */
-
-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/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.es6"></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.es6"></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
@ -1,8 +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="../bower_components/yjs/y.es6"></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'
-    // 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.es6"></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/Examples/bower.json
+++ b/Examples/bower.json
@ -1,29 +0,0 @@
-{
-  "name": "yjs-examples",
-  "version": "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/package.json
+++ b/Examples/package.json
@ -1,10 +0,0 @@
-{
-  "name": "examples",
-  "version": "1.0.0",
-  "description": "",
-  "author": "Kevin Jahns",
-  "license": "MIT",
-  "dependencies": {
-    "monaco-editor": "^0.8.3"
-  }
-}
--- a/INTERNALS.md
+++ b/INTERNALS.md
@ -0,0 +1,179 @@
+# Yjs Internals
+
+This document roughly explains how Yjs works internally. There is a complete
+walkthrough of the Yjs codebase available as a recording:
+https://youtu.be/0l5XgnQ6rB4
+
+The Yjs CRDT algorithm is described in the [YATA
+paper](https://www.researchgate.net/publication/310212186_Near_Real-Time_Peer-to-Peer_Shared_Editing_on_Extensible_Data_Types)
+from 2016. For an algorithmic view of how it works, the paper is a reasonable
+place to start. There are a handful of small improvements implemented in Yjs
+which aren't described in the paper. The most notable is that items have an
+`originRight` as well as an `origin` property, which improves performance when
+many concurrent inserts happen after the same character.
+
+At its heart, Yjs is a list CRDT. Everything is squeezed into a list in order to
+reuse the CRDT resolution algorithm:
+
+- Arrays are easy - they're lists of arbitrary items.
+- Text is a list of characters, optionally punctuated by formatting markers and
+  embeds for rich text support. Several characters can be wrapped in a single
+linked list `Item` (this is also known as the compound representation of
+CRDTs). More information about this in [this blog
+article](https://blog.kevinjahns.de/are-crdts-suitable-for-shared-editing/).
+- Maps are lists of entries. The last inserted entry for each key is used, and
+  all other duplicates for each key are flagged as deleted.
+
+Each client is assigned a unique *clientID* property on first insert. This is a
+random 53-bit integer (53 bits because that fits in the javascript safe integer
+range \[JavaScript uses IEEE 754 floats\]).
+
+## List items
+
+Each item in a Yjs list is made up of two objects:
+
+- An `Item` (*src/structs/Item.js*). This is used to relate the item to other
+  adjacent items.
+- An object in the `AbstractType` hierarchy (subclasses of
+  *src/types/AbstractType.js* - eg `YText`). This stores the actual content in
+the Yjs document.
+
+The item and type object pair have a 1-1 mapping. The item's `content` field
+references the AbstractType object and the AbstractType object's `_item` field
+references the item.
+
+Everything inserted in a Yjs document is given a unique ID, formed from a
+*ID(clientID, clock)* pair (also known as a [Lamport
+Timestamp](https://en.wikipedia.org/wiki/Lamport_timestamp)). The clock counts
+up from 0 with the first inserted character or item a client makes. This is
+similar to automerge's operation IDs, but note that the clock is only
+incremented by inserts. Deletes are handled in a very different way (see
+below).
+
+If a run of characters is inserted into a document (eg `"abc"`), the clock will
+be incremented for each character (eg 3 times here). But Yjs will only add a
+single `Item` into the list. This has no effect on the core CRDT algorithm, but
+the optimization dramatically decreases the number of javascript objects
+created during normal text editing. This optimization only applies if the
+characters share the same clientID, they're inserted in order, and all
+characters have either been deleted or all characters are not deleted. The item
+will be split if the run is interrupted for any reason (eg a character in the
+middle of the run is deleted).
+
+When an item is created, it stores a reference to the IDs of the preceding and
+succeeding item. These are stored in the item's `origin` and `originRight`
+fields, respectively. These are used when peers concurrently insert at the same
+location in a document. Though quite rare in practice, Yjs needs to make sure
+the list items always resolve to the same order on all peers. The actual logic
+is relatively simple - its only a couple dozen lines of code and it lives in
+the `Item#integrate()` method. The YATA paper has much more detail on this
+algorithm.
+
+### Item Storage
+
+The items themselves are stored in two data structures and a cache:
+
+- The items are stored in a tree of doubly-linked lists in *document order*.
+  Each item has `left` and `right` properties linking to its siblings in the
+document. Items also have a `parent` property to reference their parent in the
+document tree (null at the root). (And you can access an item's children, if
+any, through `item.content`).
+- All items are referenced in *insertion order* inside the struct store
+  (*src/utils/StructStore.js*). This references the list of items inserted by
+for each client, in chronological order. This is used to find an item in the
+tree with a given ID (using a binary search). It is also used to efficiently
+gather the operations a peer is missing during sync (more on this below).
+
+When a local insert happens, Yjs needs to map the insert position in the
+document (eg position 1000) to an ID. With just the linked list, this would
+require a slow O(n) linear scan of the list. But when editing a document, most
+inserts are either at the same position as the last insert, or nearby. To
+improve performance, Yjs stores a cache of the 80 most recently looked up
+insert positions in the document. This is consulted and updated when a position
+is looked up to improve performance in the average case. The cache is updated
+using a heuristic that is still changing (currently, it is updated when a new
+position significantly diverges from existing markers in the cache). Internally
+this is referred to as the skip list / fast search marker.
+
+### Deletions
+
+Deletions in Yjs are treated very differently from insertions. Insertions are
+implemented as a sequential operation based CRDT, but deletions are treated as
+a simpler state based CRDT.
+
+When an item has been deleted by any peer, at any point in history, it is
+flagged as deleted on the item. (Internally Yjs uses the `info` bitfield.) Yjs
+does not record metadata about a deletion:
+
+- No data is kept on *when* an item was deleted, or which user deleted it.
+- The struct store does not contain deletion records
+- The clientID's clock is not incremented
+
+If garbage collection is enabled in Yjs, when an object is deleted its content
+is discarded. If a deleted object contains children (eg a field is deleted in
+an object), the content is replaced with a `GC` object (*src/structs/GC.js*).
+This is a very lightweight structure - it only stores the length of the removed
+content.
+
+Yjs has some special logic to share which content in a document has been
+deleted:
+
+- When a delete happens, as well as marking the item, the deleted IDs are
+  listed locally within the transaction. (See below for more information about
+transactions.) When a transaction has been committed locally, the set of
+deleted items is appended to a transaction's update message.
+- A snapshot (a marked point in time in the Yjs history) is specified using
+  both the set of (clientID, clock) pairs *and* the set of all deleted item
+IDs. The deleted set is O(n), but because deletions usually happen in runs,
+this data set is usually tiny in practice. (The real world editing trace from
+the B4 benchmark document contains 182k inserts and 77k deleted characters. The
+deleted set size in a snapshot is only 4.5Kb).
+
+## Transactions
+
+All updates in Yjs happen within a *transaction*. (Defined in
+*src/utils/Transaction.js*.)
+
+The transaction collects a set of updates to the Yjs document to be applied on
+remote peers atomically. Once a transaction has been committed locally, it
+generates a compressed *update message* which is broadcast to synchronized
+remote peers to notify them of the local change. The update message contains:
+
+- The set of newly inserted items
+- The set of items deleted within the transaction.
+
+## Network protocol
+
+The network protocol is not really a part of Yjs. There are a few relevant
+concepts that can be used to create a custom network protocol:
+
+* `update`: The Yjs document can be encoded to an *update* object that can be
+  parsed to reconstruct the document. Also every change on the document fires
+an incremental document update that allows clients to sync with each other.
+The update object is a Uint8Array that efficiently encodes `Item` objects and
+the delete set.
+* `state vector`: A state vector defines the known state of each user (a set of
+  tuples `(client, clock)`). This object is also efficiently encoded as a
+Uint8Array.
+
+The client can ask a remote client for missing document updates by sending
+their state vector (often referred to as *sync step 1*). The remote peer can
+compute the missing `Item` objects using the `clocks` of the respective clients
+and compute a minimal update message that reflects all missing updates (sync
+step 2).
+
+An implementation of the syncing process is in
+[y-protocols](https://github.com/yjs/y-protocols).
+
+## Snapshots
+
+A snapshot can be used to restore an old document state. It is a `state vector`
+\+ `delete set`. A client can restore an old document state by iterating through
+the sequence CRDT and ignoring all Items that have an `id.clock >
+stateVector[id.client].clock`. Instead of using `item.deleted` the client will
+use the delete set to find out if an item was deleted or not.
+
+It is not recommended to restore an old document state using snapshots,
+although that would certainly be possible. Instead, the old state should be
+computed by iterating through the newest state and using the additional
+information from the state vector.
--- a/4
+++ b/4
@ -1,7 +1,7 @@
 The MIT License (MIT)

-Copyright (c) 2014
-  - Kevin Jahns <kevin.jahns@rwth-aachen.de>.
+Copyright (c) 2023
+  - Kevin Jahns <kevin.jahns@protonmail.com>.
  - Chair of Computer Science 5 (Databases & Information Systems), RWTH Aachen University, Germany

 Permission is hereby granted, free of charge, to any person obtaining a copy
--- a/README.md
+++ b/README.md
--- a/bower.json
+++ b/bower.json
@ -1,21 +0,0 @@
-{
-  "name": "yjs",
-  "version": "12.3.3",
-  "homepage": "y-js.org",
-  "authors": [
-    "Kevin Jahns <kevin.jahns@rwth-aachen.de>"
-  ],
-  "description": "A Framework for shared editing on any data",
-  "main": "./y.js",
-  "keywords": [
-    "Yjs",
-    "OT",
-    "Collaboration",
-    "Synchronization",
-    "ShareJS",
-    "Coweb",
-    "Concurrency"
-  ],
-  "license": "MIT",
-  "ignore": []
-}
--- a/funding.json
+++ b/funding.json
@ -0,0 +1,142 @@
+{
+  "version": "v1.0.0",
+  "entity": {
+    "type": "group",
+    "role": "steward",
+    "name": "Kevin Jahns",
+    "email": "kevin.jahns@protonmail.com",
+    "phone": "",
+    "description": "OSS Developer",
+    "webpageUrl": {
+      "url": "https://github.com/yjs"
+    }
+  },
+  "projects": [
+    {
+      "guid": "yjs",
+      "name": "Yjs",
+      "description": "A library for building collaborative applications. #p2p #local-first #CRDT Funding this project will also enable me to maintain the other Yjs-related technologies.",
+      "webpageUrl": {
+        "url": "https://github.com/yjs/yjs"
+      },
+      "repositoryUrl": {
+        "url": "https://github.com/yjs/yjs"
+      },
+      "licenses": [
+        "spdx:MIT"
+      ],
+      "tags": [
+        "collaboration",
+        "p2p",
+        "CRDT",
+        "rich-text",
+        "real-time"
+      ]
+    },
+    {
+      "guid": "Titanic",
+      "name": "Y/Titanic",
+      "description": "A provider for syncing millions of docs efficiently with other peers. This will become the foundation for building real local-first apps with Yjs.",
+      "webpageUrl": {
+        "url": "https://github.com/yjs/titanic",
+        "wellKnown": "https://github.com/yjs/titanic/blob/main/.well-known/funding-manifest-urls"
+      },
+      "repositoryUrl": {
+        "url": "https://github.com/yjs/titanic",
+        "wellKnown": "https://github.com/yjs/titanic/blob/main/.well-known/funding-manifest-urls"
+      },
+      "licenses": [
+        "spdx:MIT"
+      ],
+      "tags": [
+        "privacy",
+        "collaboration",
+        "p2p",
+        "CRDT",
+        "rich-text",
+        "real-time",
+        "web-development"
+      ]
+    }
+  ],
+  "funding": {
+    "channels": [
+      {
+        "guid": "github-sponsors",
+        "type": "payment-provider",
+        "address": "",
+        "description": "For funding of the Yjs project"
+      },
+      {
+        "guid": "y-collective",
+        "type": "payment-provider",
+        "address": "https://opencollective.com/y-collective",
+        "description": "For funding the Y-CRDT - the Rust implementation of Yjs and other listed projects."
+      }
+    ],
+    "plans": [
+      {
+        "guid": "supporter",
+        "status": "active",
+        "name": "Supporter",
+        "description": "",
+        "amount": 0,
+        "currency": "USD",
+        "frequency": "monthly",
+        "channels": [
+          "github-sponsors",
+          "y-collective"
+        ]
+      },
+      {
+        "guid": "titanic-funding",
+        "status": "active",
+        "name": "Titanic Funding",
+        "description": "Fund the next generation of local-first providers.",
+        "amount": 30000,
+        "currency": "USD",
+        "frequency": "one-time",
+        "channels": [
+          "github-sponsors"
+        ]
+      },
+      {
+        "guid": "bronze-sponsor",
+        "status": "active",
+        "name": "Bronze Sponsor",
+        "description": "This is the recommended plan for companies that use Yjs.",
+        "amount": 500,
+        "currency": "USD",
+        "frequency": "monthly",
+        "channels": [
+          "github-sponsors"
+        ]
+      },
+      {
+        "guid": "silver-sponsor",
+        "status": "active",
+        "name": "Silver Sponsor",
+        "description": "This is the recommended plan for large/successfull companies that use Yjs.",
+        "amount": 1000,
+        "currency": "USD",
+        "frequency": "monthly",
+        "channels": [
+          "github-sponsors"
+        ]
+      },
+      {
+        "guid": "gold-sponsor",
+        "status": "active",
+        "name": "Gold Sponsor",
+        "description": "This is the recommended plan for successful companies that build their entire product around Yjs-related technologies.",
+        "amount": 3000,
+        "currency": "USD",
+        "frequency": "monthly",
+        "channels": [
+          "github-sponsors"
+        ]
+      }
+    ],
+    "history": null
+  }
+}
--- a/package-lock.json
+++ b/package-lock.json
--- a/package.json
+++ b/package.json
@ -0,0 +1,99 @@
+{
+  "name": "yjs",
+  "version": "13.6.24",
+  "description": "Shared Editing Library",
+  "main": "./dist/yjs.cjs",
+  "module": "./dist/yjs.mjs",
+  "types": "./dist/src/index.d.ts",
+  "type": "module",
+  "sideEffects": false,
+  "funding": {
+    "type": "GitHub Sponsors ❤",
+    "url": "https://github.com/sponsors/dmonad"
+  },
+  "scripts": {
+    "clean": "rm -rf dist docs",
+    "test": "npm run dist && NODE_ENV=development node ./dist/tests.cjs --repetition-time 50",
+    "test-extensive": "npm run lint && npm run dist && node ./dist/tests.cjs --production --repetition-time 10000",
+    "dist": "npm run clean && rollup -c && tsc",
+    "watch": "rollup -wc",
+    "lint": "markdownlint README.md && standard && tsc",
+    "docs": "rm -rf docs; jsdoc --configure ./.jsdoc.json --verbose --readme ./README.md --package ./package.json || true",
+    "serve-docs": "npm run docs && http-server ./docs/",
+    "preversion": "npm run lint && PRODUCTION=1 npm run dist && npm run docs && node ./dist/tests.cjs --repetition-time 1000 && test -e dist/src/index.d.ts && test -e dist/yjs.cjs && test -e dist/yjs.cjs",
+    "debug": "concurrently 'http-server -o test.html' 'npm run watch'",
+    "trace-deopt": "clear && rollup -c  && node --trace-deopt dist/test.cjs",
+    "trace-opt": "clear && rollup -c  && node --trace-opt dist/test.cjs"
+  },
+  "exports": {
+    ".": {
+      "types": "./dist/src/index.d.ts",
+      "module": "./dist/yjs.mjs",
+      "import": "./dist/yjs.mjs",
+      "require": "./dist/yjs.cjs"
+    },
+    "./src/index.js": "./src/index.js",
+    "./tests/testHelper.js": "./tests/testHelper.js",
+    "./testHelper": "./dist/testHelper.mjs",
+    "./package.json": "./package.json"
+  },
+  "files": [
+    "dist/yjs.*",
+    "dist/src",
+    "src",
+    "tests/testHelper.js",
+    "dist/testHelper.mjs",
+    "sponsor-y.js"
+  ],
+  "dictionaries": {
+    "test": "tests"
+  },
+  "standard": {
+    "ignore": [
+      "/dist",
+      "/node_modules",
+      "/docs"
+    ]
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/yjs/yjs.git"
+  },
+  "keywords": [
+    "Yjs",
+    "CRDT",
+    "offline",
+    "offline-first",
+    "shared-editing",
+    "concurrency",
+    "collaboration"
+  ],
+  "author": "Kevin Jahns",
+  "email": "kevin.jahns@protonmail.com",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/yjs/yjs/issues"
+  },
+  "homepage": "https://docs.yjs.dev",
+  "dependencies": {
+    "lib0": "^0.2.99"
+  },
+  "devDependencies": {
+    "@rollup/plugin-commonjs": "^24.0.1",
+    "@rollup/plugin-node-resolve": "^15.0.1",
+    "@types/node": "^18.15.5",
+    "concurrently": "^3.6.1",
+    "http-server": "^0.12.3",
+    "jsdoc": "^3.6.7",
+    "markdownlint-cli": "^0.41.0",
+    "rollup": "^3.20.0",
+    "standard": "^16.0.4",
+    "tui-jsdoc-template": "^1.2.2",
+    "typescript": "^4.9.5",
+    "y-protocols": "^1.0.5"
+  },
+  "engines": {
+    "npm": ">=8.0.0",
+    "node": ">=16.0.0"
+  }
+}
--- a/rollup.config.js
+++ b/rollup.config.js
@ -0,0 +1,106 @@
+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
+  },
+  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/testHelper.js',
+  output: {
+    name: 'Y',
+    file: 'dist/testHelper.mjs',
+    format: 'esm',
+    sourcemap: true
+  },
+  external: id => /^lib0\//.test(id) || id === 'yjs',
+  plugins: [{
+    resolveId (importee) {
+      if (importee === '../src/index.js') {
+        return 'yjs'
+      }
+      return null
+    }
+  }]
+}, {
+  input: './tests/index.js',
+  output: {
+    name: 'test',
+    file: 'dist/tests.js',
+    format: 'iife',
+    sourcemap: true
+  },
+  plugins: [
+    debugResolve,
+    nodeResolve({
+      mainFields: ['browser', 'module', 'main']
+    }),
+    commonjs()
+  ]
+}, {
+  input: './tests/index.js',
+  output: {
+    name: 'test',
+    file: 'dist/tests.cjs',
+    format: 'cjs',
+    sourcemap: true
+  },
+  plugins: [
+    debugResolve,
+    nodeResolve({
+      mainFields: ['node', 'module', 'main'],
+      exportConditions: ['node', 'module', 'import', 'default']
+    }),
+    commonjs()
+  ],
+  external: id => /^lib0\//.test(id)
+}]
--- a/src/index.js
+++ b/src/index.js
@ -0,0 +1,135 @@
+/** eslint-env browser */
+
+export {
+  Doc,
+  Transaction,
+  YArray as Array,
+  YMap as Map,
+  YText as Text,
+  YXmlText as XmlText,
+  YXmlHook as XmlHook,
+  YXmlElement as XmlElement,
+  YXmlFragment as XmlFragment,
+  YXmlEvent,
+  YMapEvent,
+  YArrayEvent,
+  YTextEvent,
+  YEvent,
+  Item,
+  AbstractStruct,
+  GC,
+  Skip,
+  ContentBinary,
+  ContentDeleted,
+  ContentDoc,
+  ContentEmbed,
+  ContentFormat,
+  ContentJSON,
+  ContentAny,
+  ContentString,
+  ContentType,
+  AbstractType,
+  getTypeChildren,
+  createRelativePositionFromTypeIndex,
+  createRelativePositionFromJSON,
+  createAbsolutePositionFromRelativePosition,
+  compareRelativePositions,
+  AbsolutePosition,
+  RelativePosition,
+  ID,
+  createID,
+  compareIDs,
+  getState,
+  Snapshot,
+  createSnapshot,
+  createDeleteSet,
+  createDeleteSetFromStructStore,
+  cleanupYTextFormatting,
+  snapshot,
+  emptySnapshot,
+  findRootTypeKey,
+  findIndexSS,
+  getItem,
+  getItemCleanStart,
+  getItemCleanEnd,
+  typeListToArraySnapshot,
+  typeMapGetSnapshot,
+  typeMapGetAllSnapshot,
+  createDocFromSnapshot,
+  iterateDeletedStructs,
+  applyUpdate,
+  applyUpdateV2,
+  readUpdate,
+  readUpdateV2,
+  encodeStateAsUpdate,
+  encodeStateAsUpdateV2,
+  encodeStateVector,
+  UndoManager,
+  decodeSnapshot,
+  encodeSnapshot,
+  decodeSnapshotV2,
+  encodeSnapshotV2,
+  decodeStateVector,
+  logUpdate,
+  logUpdateV2,
+  decodeUpdate,
+  decodeUpdateV2,
+  relativePositionToJSON,
+  isDeleted,
+  isParentOf,
+  equalSnapshots,
+  PermanentUserData, // @TODO experimental
+  tryGc,
+  transact,
+  AbstractConnector,
+  logType,
+  mergeUpdates,
+  mergeUpdatesV2,
+  parseUpdateMeta,
+  parseUpdateMetaV2,
+  encodeStateVectorFromUpdate,
+  encodeStateVectorFromUpdateV2,
+  encodeRelativePosition,
+  decodeRelativePosition,
+  diffUpdate,
+  diffUpdateV2,
+  convertUpdateFormatV1ToV2,
+  convertUpdateFormatV2ToV1,
+  obfuscateUpdate,
+  obfuscateUpdateV2,
+  UpdateEncoderV1,
+  UpdateEncoderV2,
+  UpdateDecoderV1,
+  UpdateDecoderV2,
+  equalDeleteSets,
+  mergeDeleteSets,
+  snapshotContainsUpdate
+} from './internals.js'
+
+const glo = /** @type {any} */ (typeof globalThis !== 'undefined'
+  ? globalThis
+  : typeof window !== 'undefined'
+    ? window
+    // @ts-ignore
+    : typeof global !== 'undefined' ? global : {})
+
+const importIdentifier = '__ $YJS$ __'
+
+if (glo[importIdentifier] === true) {
+  /**
+   * Dear reader of this message. Please take this seriously.
+   *
+   * If you see this message, make sure that you only import one version of Yjs. In many cases,
+   * your package manager installs two versions of Yjs that are used by different packages within your project.
+   * Another reason for this message is that some parts of your project use the commonjs version of Yjs
+   * and others use the EcmaScript version of Yjs.
+   *
+   * This often leads to issues that are hard to debug. We often need to perform constructor checks,
+   * e.g. `struct instanceof GC`. If you imported different versions of Yjs, it is impossible for us to
+   * do the constructor checks anymore - which might break the CRDT algorithm.
+   *
+   * https://github.com/yjs/yjs/issues/438
+   */
+  console.error('Yjs was already imported. This breaks constructor checks and will lead to issues! - https://github.com/yjs/yjs/issues/438')
+}
+glo[importIdentifier] = true
--- a/src/internals.js
+++ b/src/internals.js
@ -0,0 +1,42 @@
+export * from './utils/AbstractConnector.js'
+export * from './utils/DeleteSet.js'
+export * from './utils/Doc.js'
+export * from './utils/UpdateDecoder.js'
+export * from './utils/UpdateEncoder.js'
+export * from './utils/encoding.js'
+export * from './utils/EventHandler.js'
+export * from './utils/ID.js'
+export * from './utils/isParentOf.js'
+export * from './utils/logging.js'
+export * from './utils/PermanentUserData.js'
+export * from './utils/RelativePosition.js'
+export * from './utils/Snapshot.js'
+export * from './utils/StructStore.js'
+export * from './utils/Transaction.js'
+export * from './utils/UndoManager.js'
+export * from './utils/updates.js'
+export * from './utils/YEvent.js'
+
+export * from './types/AbstractType.js'
+export * from './types/YArray.js'
+export * from './types/YMap.js'
+export * from './types/YText.js'
+export * from './types/YXmlFragment.js'
+export * from './types/YXmlElement.js'
+export * from './types/YXmlEvent.js'
+export * from './types/YXmlHook.js'
+export * from './types/YXmlText.js'
+
+export * from './structs/AbstractStruct.js'
+export * from './structs/GC.js'
+export * from './structs/ContentBinary.js'
+export * from './structs/ContentDeleted.js'
+export * from './structs/ContentDoc.js'
+export * from './structs/ContentEmbed.js'
+export * from './structs/ContentFormat.js'
+export * from './structs/ContentJSON.js'
+export * from './structs/ContentAny.js'
+export * from './structs/ContentString.js'
+export * from './structs/ContentType.js'
+export * from './structs/Item.js'
+export * from './structs/Skip.js'
--- a/src/structs/AbstractStruct.js
+++ b/src/structs/AbstractStruct.js
@ -0,0 +1,51 @@
+import {
+  UpdateEncoderV1, UpdateEncoderV2, ID, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+export class AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {number} length
+   */
+  constructor (id, length) {
+    this.id = id
+    this.length = length
+  }
+
+  /**
+   * @type {boolean}
+   */
+  get deleted () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * Merge this struct with the item to the right.
+   * This method is already assuming that `this.id.clock + this.length === this.id.clock`.
+   * Also this method does *not* remove right from StructStore!
+   * @param {AbstractStruct} right
+   * @return {boolean} whether this merged with right
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   * @param {number} offset
+   * @param {number} encodingRef
+   */
+  write (encoder, offset, encodingRef) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    throw error.methodUnimplemented()
+  }
+}
--- a/src/structs/ContentAny.js
+++ b/src/structs/ContentAny.js
@ -0,0 +1,114 @@
+import {
+  UpdateEncoderV1, UpdateEncoderV2, UpdateDecoderV1, UpdateDecoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as env from 'lib0/environment'
+import * as object from 'lib0/object'
+
+const isDevMode = env.getVariable('node_env') === 'development'
+
+export class ContentAny {
+  /**
+   * @param {Array<any>} arr
+   */
+  constructor (arr) {
+    /**
+     * @type {Array<any>}
+     */
+    this.arr = arr
+    isDevMode && object.deepFreeze(arr)
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.arr.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.arr
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentAny}
+   */
+  copy () {
+    return new ContentAny(this.arr)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentAny}
+   */
+  splice (offset) {
+    const right = new ContentAny(this.arr.slice(offset))
+    this.arr = this.arr.slice(0, offset)
+    return right
+  }
+
+  /**
+   * @param {ContentAny} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.arr = this.arr.concat(right.arr)
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoder.writeLen(len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoder.writeAny(c)
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 8
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentAny}
+ */
+export const readContentAny = decoder => {
+  const len = decoder.readLen()
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    cs.push(decoder.readAny())
+  }
+  return new ContentAny(cs)
+}
--- a/src/structs/ContentBinary.js
+++ b/src/structs/ContentBinary.js
@ -0,0 +1,92 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+export class ContentBinary {
+  /**
+   * @param {Uint8Array} content
+   */
+  constructor (content) {
+    this.content = content
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.content]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentBinary}
+   */
+  copy () {
+    return new ContentBinary(this.content)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentBinary}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentBinary} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeBuf(this.content)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 3
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2 } decoder
+ * @return {ContentBinary}
+ */
+export const readContentBinary = decoder => new ContentBinary(decoder.readBuf())
--- a/src/structs/ContentDeleted.js
+++ b/src/structs/ContentDeleted.js
@ -0,0 +1,100 @@
+import {
+  addToDeleteSet,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+export class ContentDeleted {
+  /**
+   * @param {number} len
+   */
+  constructor (len) {
+    this.len = len
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.len
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return []
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return false
+  }
+
+  /**
+   * @return {ContentDeleted}
+   */
+  copy () {
+    return new ContentDeleted(this.len)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentDeleted}
+   */
+  splice (offset) {
+    const right = new ContentDeleted(this.len - offset)
+    this.len = offset
+    return right
+  }
+
+  /**
+   * @param {ContentDeleted} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.len += right.len
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    addToDeleteSet(transaction.deleteSet, item.id.client, item.id.clock, this.len)
+    item.markDeleted()
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeLen(this.len - offset)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 1
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2 } decoder
+ * @return {ContentDeleted}
+ */
+export const readContentDeleted = decoder => new ContentDeleted(decoder.readLen())
--- a/src/structs/ContentDoc.js
+++ b/src/structs/ContentDoc.js
@ -0,0 +1,140 @@
+import {
+  Doc, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @param {string} guid
+ * @param {Object<string, any>} opts
+ */
+const createDocFromOpts = (guid, opts) => new Doc({ guid, ...opts, shouldLoad: opts.shouldLoad || opts.autoLoad || false })
+
+/**
+ * @private
+ */
+export class ContentDoc {
+  /**
+   * @param {Doc} doc
+   */
+  constructor (doc) {
+    if (doc._item) {
+      console.error('This document was already integrated as a sub-document. You should create a second instance instead with the same guid.')
+    }
+    /**
+     * @type {Doc}
+     */
+    this.doc = doc
+    /**
+     * @type {any}
+     */
+    const opts = {}
+    this.opts = opts
+    if (!doc.gc) {
+      opts.gc = false
+    }
+    if (doc.autoLoad) {
+      opts.autoLoad = true
+    }
+    if (doc.meta !== null) {
+      opts.meta = doc.meta
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.doc]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentDoc}
+   */
+  copy () {
+    return new ContentDoc(createDocFromOpts(this.doc.guid, this.opts))
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentDoc}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentDoc} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {
+    // this needs to be reflected in doc.destroy as well
+    this.doc._item = item
+    transaction.subdocsAdded.add(this.doc)
+    if (this.doc.shouldLoad) {
+      transaction.subdocsLoaded.add(this.doc)
+    }
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    if (transaction.subdocsAdded.has(this.doc)) {
+      transaction.subdocsAdded.delete(this.doc)
+    } else {
+      transaction.subdocsRemoved.add(this.doc)
+    }
+  }
+
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) { }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeString(this.doc.guid)
+    encoder.writeAny(this.opts)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 9
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentDoc}
+ */
+export const readContentDoc = decoder => new ContentDoc(createDocFromOpts(decoder.readString(), decoder.readAny()))
--- a/src/structs/ContentEmbed.js
+++ b/src/structs/ContentEmbed.js
@ -0,0 +1,97 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Item, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @private
+ */
+export class ContentEmbed {
+  /**
+   * @param {Object} embed
+   */
+  constructor (embed) {
+    this.embed = embed
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return [this.embed]
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentEmbed}
+   */
+  copy () {
+    return new ContentEmbed(this.embed)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentEmbed}
+   */
+  splice (offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentEmbed} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeJSON(this.embed)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 5
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentEmbed}
+ */
+export const readContentEmbed = decoder => new ContentEmbed(decoder.readJSON())
--- a/src/structs/ContentFormat.js
+++ b/src/structs/ContentFormat.js
@ -0,0 +1,104 @@
+import {
+  YText, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Item, StructStore, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @private
+ */
+export class ContentFormat {
+  /**
+   * @param {string} key
+   * @param {Object} value
+   */
+  constructor (key, value) {
+    this.key = key
+    this.value = value
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return 1
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return []
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return false
+  }
+
+  /**
+   * @return {ContentFormat}
+   */
+  copy () {
+    return new ContentFormat(this.key, this.value)
+  }
+
+  /**
+   * @param {number} _offset
+   * @return {ContentFormat}
+   */
+  splice (_offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {ContentFormat} _right
+   * @return {boolean}
+   */
+  mergeWith (_right) {
+    return false
+  }
+
+  /**
+   * @param {Transaction} _transaction
+   * @param {Item} item
+   */
+  integrate (_transaction, item) {
+    // @todo searchmarker are currently unsupported for rich text documents
+    const p = /** @type {YText} */ (item.parent)
+    p._searchMarker = null
+    p._hasFormatting = true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeKey(this.key)
+    encoder.writeJSON(this.value)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 6
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentFormat}
+ */
+export const readContentFormat = decoder => new ContentFormat(decoder.readKey(), decoder.readJSON())
--- a/src/structs/ContentJSON.js
+++ b/src/structs/ContentJSON.js
@ -0,0 +1,118 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @private
+ */
+export class ContentJSON {
+  /**
+   * @param {Array<any>} arr
+   */
+  constructor (arr) {
+    /**
+     * @type {Array<any>}
+     */
+    this.arr = arr
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.arr.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.arr
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentJSON}
+   */
+  copy () {
+    return new ContentJSON(this.arr)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentJSON}
+   */
+  splice (offset) {
+    const right = new ContentJSON(this.arr.slice(offset))
+    this.arr = this.arr.slice(0, offset)
+    return right
+  }
+
+  /**
+   * @param {ContentJSON} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.arr = this.arr.concat(right.arr)
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const len = this.arr.length
+    encoder.writeLen(len - offset)
+    for (let i = offset; i < len; i++) {
+      const c = this.arr[i]
+      encoder.writeString(c === undefined ? 'undefined' : JSON.stringify(c))
+    }
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 2
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentJSON}
+ */
+export const readContentJSON = decoder => {
+  const len = decoder.readLen()
+  const cs = []
+  for (let i = 0; i < len; i++) {
+    const c = decoder.readString()
+    if (c === 'undefined') {
+      cs.push(undefined)
+    } else {
+      cs.push(JSON.parse(c))
+    }
+  }
+  return new ContentJSON(cs)
+}
--- a/src/structs/ContentString.js
+++ b/src/structs/ContentString.js
@ -0,0 +1,112 @@
+import {
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Transaction, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @private
+ */
+export class ContentString {
+  /**
+   * @param {string} str
+   */
+  constructor (str) {
+    /**
+     * @type {string}
+     */
+    this.str = str
+  }
+
+  /**
+   * @return {number}
+   */
+  getLength () {
+    return this.str.length
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    return this.str.split('')
+  }
+
+  /**
+   * @return {boolean}
+   */
+  isCountable () {
+    return true
+  }
+
+  /**
+   * @return {ContentString}
+   */
+  copy () {
+    return new ContentString(this.str)
+  }
+
+  /**
+   * @param {number} offset
+   * @return {ContentString}
+   */
+  splice (offset) {
+    const right = new ContentString(this.str.slice(offset))
+    this.str = this.str.slice(0, offset)
+
+    // Prevent encoding invalid documents because of splitting of surrogate pairs: https://github.com/yjs/yjs/issues/248
+    const firstCharCode = this.str.charCodeAt(offset - 1)
+    if (firstCharCode >= 0xD800 && firstCharCode <= 0xDBFF) {
+      // Last character of the left split is the start of a surrogate utf16/ucs2 pair.
+      // We don't support splitting of surrogate pairs because this may lead to invalid documents.
+      // Replace the invalid character with a unicode replacement character (<28> / U+FFFD)
+      this.str = this.str.slice(0, offset - 1) + '<27>'
+      // replace right as well
+      right.str = '<27>' + right.str.slice(1)
+    }
+    return right
+  }
+
+  /**
+   * @param {ContentString} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    this.str += right.str
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {Item} item
+   */
+  integrate (transaction, item) {}
+  /**
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {}
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {}
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeString(offset === 0 ? this.str : this.str.slice(offset))
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 4
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentString}
+ */
+export const readContentString = decoder => new ContentString(decoder.readString())
--- a/src/structs/ContentType.js
+++ b/src/structs/ContentType.js
@ -0,0 +1,171 @@
+import {
+  readYArray,
+  readYMap,
+  readYText,
+  readYXmlElement,
+  readYXmlFragment,
+  readYXmlHook,
+  readYXmlText,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, Item, YEvent, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+
+/**
+ * @type {Array<function(UpdateDecoderV1 | UpdateDecoderV2):AbstractType<any>>}
+ * @private
+ */
+export const typeRefs = [
+  readYArray,
+  readYMap,
+  readYText,
+  readYXmlElement,
+  readYXmlFragment,
+  readYXmlHook,
+  readYXmlText
+]
+
+export const YArrayRefID = 0
+export const YMapRefID = 1
+export const YTextRefID = 2
+export const YXmlElementRefID = 3
+export const YXmlFragmentRefID = 4
+export const YXmlHookRefID = 5
+export const YXmlTextRefID = 6
+
+/**
+ * @private
+ */
+export class ContentType {
+  /**
+   * @param {AbstractType<any>} 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 if (item.id.clock < (transaction.beforeState.get(item.id.client) || 0)) {
+        // This will be gc'd later and we want to merge it if possible
+        // We try to merge all deleted items after each transaction,
+        // but we have no knowledge about that this needs to be merged
+        // since it is not in transaction.ds. Hence we add it to transaction._mergeStructs
+        transaction._mergeStructs.push(item)
+      }
+      item = item.right
+    }
+    this.type._map.forEach(item => {
+      if (!item.deleted) {
+        item.delete(transaction)
+      } else if (item.id.clock < (transaction.beforeState.get(item.id.client) || 0)) {
+        // same as above
+        transaction._mergeStructs.push(item)
+      }
+    })
+    transaction.changed.delete(this.type)
+  }
+
+  /**
+   * @param {StructStore} store
+   */
+  gc (store) {
+    let item = this.type._start
+    while (item !== null) {
+      item.gc(store, true)
+      item = item.right
+    }
+    this.type._start = null
+    this.type._map.forEach(/** @param {Item | null} item */ (item) => {
+      while (item !== null) {
+        item.gc(store, true)
+        item = item.left
+      }
+    })
+    this.type._map = new Map()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    this.type._write(encoder)
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    return 7
+  }
+}
+
+/**
+ * @private
+ *
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {ContentType}
+ */
+export const readContentType = decoder => new ContentType(typeRefs[decoder.readTypeRef()](decoder))
--- a/src/structs/GC.js
+++ b/src/structs/GC.js
@ -0,0 +1,60 @@
+import {
+  AbstractStruct,
+  addStruct,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+export const structGCRefNumber = 0
+
+/**
+ * @private
+ */
+export class GC extends AbstractStruct {
+  get deleted () {
+    return true
+  }
+
+  delete () {}
+
+  /**
+   * @param {GC} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (this.constructor !== right.constructor) {
+      return false
+    }
+    this.length += right.length
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    if (offset > 0) {
+      this.id.clock += offset
+      this.length -= offset
+    }
+    addStruct(transaction.doc.store, this)
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeInfo(structGCRefNumber)
+    encoder.writeLen(this.length - offset)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    return null
+  }
+}
--- a/src/structs/Item.js
+++ b/src/structs/Item.js
@ -0,0 +1,812 @@
+import {
+  GC,
+  getState,
+  AbstractStruct,
+  replaceStruct,
+  addStruct,
+  addToDeleteSet,
+  findRootTypeKey,
+  compareIDs,
+  getItem,
+  getItemCleanEnd,
+  getItemCleanStart,
+  readContentDeleted,
+  readContentBinary,
+  readContentJSON,
+  readContentAny,
+  readContentString,
+  readContentEmbed,
+  readContentDoc,
+  createID,
+  readContentFormat,
+  readContentType,
+  addChangedTypeToTransaction,
+  isDeleted,
+  StackItem, DeleteSet, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, ContentType, ContentDeleted, StructStore, ID, AbstractType, Transaction // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+import * as binary from 'lib0/binary'
+import * as array from 'lib0/array'
+
+/**
+ * @todo This should return several items
+ *
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {{item:Item, diff:number}}
+ */
+export const followRedone = (store, id) => {
+  /**
+   * @type {ID|null}
+   */
+  let nextID = id
+  let diff = 0
+  let item
+  do {
+    if (diff > 0) {
+      nextID = createID(nextID.client, nextID.clock + diff)
+    }
+    item = getItem(store, nextID)
+    diff = nextID.clock - item.id.clock
+    nextID = item.redone
+  } while (nextID !== null && item instanceof Item)
+  return {
+    item, diff
+  }
+}
+
+/**
+ * Make sure that neither item nor any of its parents is ever deleted.
+ *
+ * This property does not persist when storing it into a database or when
+ * sending it to other peers
+ *
+ * @param {Item|null} item
+ * @param {boolean} keep
+ */
+export const keepItem = (item, keep) => {
+  while (item !== null && item.keep !== keep) {
+    item.keep = keep
+    item = /** @type {AbstractType<any>} */ (item.parent)._item
+  }
+}
+
+/**
+ * Split leftItem into two items
+ * @param {Transaction} transaction
+ * @param {Item} leftItem
+ * @param {number} diff
+ * @return {Item}
+ *
+ * @function
+ * @private
+ */
+export const splitItem = (transaction, leftItem, diff) => {
+  // create rightItem
+  const { client, clock } = leftItem.id
+  const rightItem = new Item(
+    createID(client, clock + diff),
+    leftItem,
+    createID(client, clock + diff - 1),
+    leftItem.right,
+    leftItem.rightOrigin,
+    leftItem.parent,
+    leftItem.parentSub,
+    leftItem.content.splice(diff)
+  )
+  if (leftItem.deleted) {
+    rightItem.markDeleted()
+  }
+  if (leftItem.keep) {
+    rightItem.keep = true
+  }
+  if (leftItem.redone !== null) {
+    rightItem.redone = createID(leftItem.redone.client, leftItem.redone.clock + diff)
+  }
+  // update left (do not set leftItem.rightOrigin as it will lead to problems when syncing)
+  leftItem.right = rightItem
+  // update right
+  if (rightItem.right !== null) {
+    rightItem.right.left = rightItem
+  }
+  // right is more specific.
+  transaction._mergeStructs.push(rightItem)
+  // update parent._map
+  if (rightItem.parentSub !== null && rightItem.right === null) {
+    /** @type {AbstractType<any>} */ (rightItem.parent)._map.set(rightItem.parentSub, rightItem)
+  }
+  leftItem.length = diff
+  return rightItem
+}
+
+/**
+ * @param {Array<StackItem>} stack
+ * @param {ID} id
+ */
+const isDeletedByUndoStack = (stack, id) => array.some(stack, /** @param {StackItem} s */ s => isDeleted(s.deletions, id))
+
+/**
+ * Redoes the effect of this operation.
+ *
+ * @param {Transaction} transaction The Yjs instance.
+ * @param {Item} item
+ * @param {Set<Item>} redoitems
+ * @param {DeleteSet} itemsToDelete
+ * @param {boolean} ignoreRemoteMapChanges
+ * @param {import('../utils/UndoManager.js').UndoManager} um
+ *
+ * @return {Item|null}
+ *
+ * @private
+ */
+export const redoItem = (transaction, item, redoitems, itemsToDelete, ignoreRemoteMapChanges, um) => {
+  const doc = transaction.doc
+  const store = doc.store
+  const ownClientID = doc.clientID
+  const redone = item.redone
+  if (redone !== null) {
+    return getItemCleanStart(transaction, redone)
+  }
+  let parentItem = /** @type {AbstractType<any>} */ (item.parent)._item
+  /**
+   * @type {Item|null}
+   */
+  let left = null
+  /**
+   * @type {Item|null}
+   */
+  let right
+  // make sure that parent is redone
+  if (parentItem !== null && parentItem.deleted === true) {
+    // try to undo parent if it will be undone anyway
+    if (parentItem.redone === null && (!redoitems.has(parentItem) || redoItem(transaction, parentItem, redoitems, itemsToDelete, ignoreRemoteMapChanges, um) === null)) {
+      return null
+    }
+    while (parentItem.redone !== null) {
+      parentItem = getItemCleanStart(transaction, parentItem.redone)
+    }
+  }
+  const parentType = parentItem === null ? /** @type {AbstractType<any>} */ (item.parent) : /** @type {ContentType} */ (parentItem.content).type
+
+  if (item.parentSub === null) {
+    // Is an array item. Insert at the old position
+    left = item.left
+    right = item
+    // find next cloned_redo items
+    while (left !== null) {
+      /**
+       * @type {Item|null}
+       */
+      let leftTrace = left
+      // trace redone until parent matches
+      while (leftTrace !== null && /** @type {AbstractType<any>} */ (leftTrace.parent)._item !== parentItem) {
+        leftTrace = leftTrace.redone === null ? null : getItemCleanStart(transaction, leftTrace.redone)
+      }
+      if (leftTrace !== null && /** @type {AbstractType<any>} */ (leftTrace.parent)._item === parentItem) {
+        left = leftTrace
+        break
+      }
+      left = left.left
+    }
+    while (right !== null) {
+      /**
+       * @type {Item|null}
+       */
+      let rightTrace = right
+      // trace redone until parent matches
+      while (rightTrace !== null && /** @type {AbstractType<any>} */ (rightTrace.parent)._item !== parentItem) {
+        rightTrace = rightTrace.redone === null ? null : getItemCleanStart(transaction, rightTrace.redone)
+      }
+      if (rightTrace !== null && /** @type {AbstractType<any>} */ (rightTrace.parent)._item === parentItem) {
+        right = rightTrace
+        break
+      }
+      right = right.right
+    }
+  } else {
+    right = null
+    if (item.right && !ignoreRemoteMapChanges) {
+      left = item
+      // Iterate right while right is in itemsToDelete
+      // If it is intended to delete right while item is redone, we can expect that item should replace right.
+      while (left !== null && left.right !== null && (left.right.redone || isDeleted(itemsToDelete, left.right.id) || isDeletedByUndoStack(um.undoStack, left.right.id) || isDeletedByUndoStack(um.redoStack, left.right.id))) {
+        left = left.right
+        // follow redone
+        while (left.redone) left = getItemCleanStart(transaction, left.redone)
+      }
+      if (left && left.right !== null) {
+        // It is not possible to redo this item because it conflicts with a
+        // change from another client
+        return null
+      }
+    } else {
+      left = parentType._map.get(item.parentSub) || null
+    }
+  }
+  const nextClock = getState(store, ownClientID)
+  const nextId = createID(ownClientID, nextClock)
+  const redoneItem = new Item(
+    nextId,
+    left, left && left.lastId,
+    right, right && right.id,
+    parentType,
+    item.parentSub,
+    item.content.copy()
+  )
+  item.redone = nextId
+  keepItem(redoneItem, true)
+  redoneItem.integrate(transaction, 0)
+  return redoneItem
+}
+
+/**
+ * Abstract class that represents any content.
+ */
+export class Item extends AbstractStruct {
+  /**
+   * @param {ID} id
+   * @param {Item | null} left
+   * @param {ID | null} origin
+   * @param {Item | null} right
+   * @param {ID | null} rightOrigin
+   * @param {AbstractType<any>|ID|null} parent Is a type if integrated, is null if it is possible to copy parent from left or right, is ID before integration to search for it.
+   * @param {string | null} parentSub
+   * @param {AbstractContent} content
+   */
+  constructor (id, left, origin, right, rightOrigin, parent, parentSub, content) {
+    super(id, content.getLength())
+    /**
+     * The item that was originally to the left of this item.
+     * @type {ID | null}
+     */
+    this.origin = origin
+    /**
+     * The item that is currently to the left of this item.
+     * @type {Item | null}
+     */
+    this.left = left
+    /**
+     * The item that is currently to the right of this item.
+     * @type {Item | null}
+     */
+    this.right = right
+    /**
+     * The item that was originally to the right of this item.
+     * @type {ID | null}
+     */
+    this.rightOrigin = rightOrigin
+    /**
+     * @type {AbstractType<any>|ID|null}
+     */
+    this.parent = parent
+    /**
+     * If the parent refers to this item with some kind of key (e.g. YMap, the
+     * key is specified here. The key is then used to refer to the list in which
+     * to insert this item. If `parentSub = null` type._start is the list in
+     * which to insert to. Otherwise it is `parent._map`.
+     * @type {String | null}
+     */
+    this.parentSub = parentSub
+    /**
+     * If this type's effect is redone this type refers to the type that undid
+     * this operation.
+     * @type {ID | null}
+     */
+    this.redone = null
+    /**
+     * @type {AbstractContent}
+     */
+    this.content = content
+    /**
+     * bit1: keep
+     * bit2: countable
+     * bit3: deleted
+     * bit4: mark - mark node as fast-search-marker
+     * @type {number} byte
+     */
+    this.info = this.content.isCountable() ? binary.BIT2 : 0
+  }
+
+  /**
+   * This is used to mark the item as an indexed fast-search marker
+   *
+   * @type {boolean}
+   */
+  set marker (isMarked) {
+    if (((this.info & binary.BIT4) > 0) !== isMarked) {
+      this.info ^= binary.BIT4
+    }
+  }
+
+  get marker () {
+    return (this.info & binary.BIT4) > 0
+  }
+
+  /**
+   * If true, do not garbage collect this Item.
+   */
+  get keep () {
+    return (this.info & binary.BIT1) > 0
+  }
+
+  set keep (doKeep) {
+    if (this.keep !== doKeep) {
+      this.info ^= binary.BIT1
+    }
+  }
+
+  get countable () {
+    return (this.info & binary.BIT2) > 0
+  }
+
+  /**
+   * Whether this item was deleted or not.
+   * @type {Boolean}
+   */
+  get deleted () {
+    return (this.info & binary.BIT3) > 0
+  }
+
+  set deleted (doDelete) {
+    if (this.deleted !== doDelete) {
+      this.info ^= binary.BIT3
+    }
+  }
+
+  markDeleted () {
+    this.info |= binary.BIT3
+  }
+
+  /**
+   * Return the creator clientID of the missing op or define missing items and return null.
+   *
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    if (this.origin && this.origin.client !== this.id.client && this.origin.clock >= getState(store, this.origin.client)) {
+      return this.origin.client
+    }
+    if (this.rightOrigin && this.rightOrigin.client !== this.id.client && this.rightOrigin.clock >= getState(store, this.rightOrigin.client)) {
+      return this.rightOrigin.client
+    }
+    if (this.parent && this.parent.constructor === ID && this.id.client !== this.parent.client && this.parent.clock >= getState(store, this.parent.client)) {
+      return this.parent.client
+    }
+
+    // We have all missing ids, now find the items
+
+    if (this.origin) {
+      this.left = getItemCleanEnd(transaction, store, this.origin)
+      this.origin = this.left.lastId
+    }
+    if (this.rightOrigin) {
+      this.right = getItemCleanStart(transaction, this.rightOrigin)
+      this.rightOrigin = this.right.id
+    }
+    if ((this.left && this.left.constructor === GC) || (this.right && this.right.constructor === GC)) {
+      this.parent = null
+    } else if (!this.parent) {
+      // only set parent if this shouldn't be garbage collected
+      if (this.left && this.left.constructor === Item) {
+        this.parent = this.left.parent
+        this.parentSub = this.left.parentSub
+      } else if (this.right && this.right.constructor === Item) {
+        this.parent = this.right.parent
+        this.parentSub = this.right.parentSub
+      }
+    } else if (this.parent.constructor === ID) {
+      const parentItem = getItem(store, this.parent)
+      if (parentItem.constructor === GC) {
+        this.parent = null
+      } else {
+        this.parent = /** @type {ContentType} */ (parentItem.content).type
+      }
+    }
+    return null
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    if (offset > 0) {
+      this.id.clock += offset
+      this.left = getItemCleanEnd(transaction, transaction.doc.store, createID(this.id.client, this.id.clock - 1))
+      this.origin = this.left.lastId
+      this.content = this.content.splice(offset)
+      this.length -= offset
+    }
+
+    if (this.parent) {
+      if ((!this.left && (!this.right || this.right.left !== null)) || (this.left && this.left.right !== this.right)) {
+        /**
+         * @type {Item|null}
+         */
+        let left = this.left
+
+        /**
+         * @type {Item|null}
+         */
+        let o
+        // set o to the first conflicting item
+        if (left !== null) {
+          o = left.right
+        } else if (this.parentSub !== null) {
+          o = /** @type {AbstractType<any>} */ (this.parent)._map.get(this.parentSub) || null
+          while (o !== null && o.left !== null) {
+            o = o.left
+          }
+        } else {
+          o = /** @type {AbstractType<any>} */ (this.parent)._start
+        }
+        // TODO: use something like DeleteSet here (a tree implementation would be best)
+        // @todo use global set definitions
+        /**
+         * @type {Set<Item>}
+         */
+        const conflictingItems = new Set()
+        /**
+         * @type {Set<Item>}
+         */
+        const itemsBeforeOrigin = new Set()
+        // Let c in conflictingItems, b in itemsBeforeOrigin
+        // ***{origin}bbbb{this}{c,b}{c,b}{o}***
+        // Note that conflictingItems is a subset of itemsBeforeOrigin
+        while (o !== null && o !== this.right) {
+          itemsBeforeOrigin.add(o)
+          conflictingItems.add(o)
+          if (compareIDs(this.origin, o.origin)) {
+            // case 1
+            if (o.id.client < this.id.client) {
+              left = o
+              conflictingItems.clear()
+            } else if (compareIDs(this.rightOrigin, o.rightOrigin)) {
+              // this and o are conflicting and point to the same integration points. The id decides which item comes first.
+              // Since this is to the left of o, we can break here
+              break
+            } // else, o might be integrated before an item that this conflicts with. If so, we will find it in the next iterations
+          } else if (o.origin !== null && itemsBeforeOrigin.has(getItem(transaction.doc.store, o.origin))) { // use getItem instead of getItemCleanEnd because we don't want / need to split items.
+            // case 2
+            if (!conflictingItems.has(getItem(transaction.doc.store, o.origin))) {
+              left = o
+              conflictingItems.clear()
+            }
+          } else {
+            break
+          }
+          o = o.right
+        }
+        this.left = left
+      }
+      // reconnect left/right + update parent map/start if necessary
+      if (this.left !== null) {
+        const right = this.left.right
+        this.right = right
+        this.left.right = this
+      } else {
+        let r
+        if (this.parentSub !== null) {
+          r = /** @type {AbstractType<any>} */ (this.parent)._map.get(this.parentSub) || null
+          while (r !== null && r.left !== null) {
+            r = r.left
+          }
+        } else {
+          r = /** @type {AbstractType<any>} */ (this.parent)._start
+          ;/** @type {AbstractType<any>} */ (this.parent)._start = this
+        }
+        this.right = r
+      }
+      if (this.right !== null) {
+        this.right.left = this
+      } else if (this.parentSub !== null) {
+        // set as current parent value if right === null and this is parentSub
+        /** @type {AbstractType<any>} */ (this.parent)._map.set(this.parentSub, this)
+        if (this.left !== null) {
+          // this is the current attribute value of parent. delete right
+          this.left.delete(transaction)
+        }
+      }
+      // adjust length of parent
+      if (this.parentSub === null && this.countable && !this.deleted) {
+        /** @type {AbstractType<any>} */ (this.parent)._length += this.length
+      }
+      addStruct(transaction.doc.store, this)
+      this.content.integrate(transaction, this)
+      // add parent to transaction.changed
+      addChangedTypeToTransaction(transaction, /** @type {AbstractType<any>} */ (this.parent), this.parentSub)
+      if ((/** @type {AbstractType<any>} */ (this.parent)._item !== null && /** @type {AbstractType<any>} */ (this.parent)._item.deleted) || (this.parentSub !== null && this.right !== null)) {
+        // delete if parent is deleted or if this is not the current attribute value of parent
+        this.delete(transaction)
+      }
+    } else {
+      // parent is not defined. Integrate GC struct instead
+      new GC(this.id, this.length).integrate(transaction, 0)
+    }
+  }
+
+  /**
+   * Returns the next non-deleted item
+   */
+  get next () {
+    let n = this.right
+    while (n !== null && n.deleted) {
+      n = n.right
+    }
+    return n
+  }
+
+  /**
+   * Returns the previous non-deleted item
+   */
+  get prev () {
+    let n = this.left
+    while (n !== null && n.deleted) {
+      n = n.left
+    }
+    return n
+  }
+
+  /**
+   * Computes the last content address of this Item.
+   */
+  get lastId () {
+    // allocating ids is pretty costly because of the amount of ids created, so we try to reuse whenever possible
+    return this.length === 1 ? this.id : createID(this.id.client, this.id.clock + this.length - 1)
+  }
+
+  /**
+   * Try to merge two items
+   *
+   * @param {Item} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (
+      this.constructor === right.constructor &&
+      compareIDs(right.origin, this.lastId) &&
+      this.right === right &&
+      compareIDs(this.rightOrigin, right.rightOrigin) &&
+      this.id.client === right.id.client &&
+      this.id.clock + this.length === right.id.clock &&
+      this.deleted === right.deleted &&
+      this.redone === null &&
+      right.redone === null &&
+      this.content.constructor === right.content.constructor &&
+      this.content.mergeWith(right.content)
+    ) {
+      const searchMarker = /** @type {AbstractType<any>} */ (this.parent)._searchMarker
+      if (searchMarker) {
+        searchMarker.forEach(marker => {
+          if (marker.p === right) {
+            // right is going to be "forgotten" so we need to update the marker
+            marker.p = this
+            // adjust marker index
+            if (!this.deleted && this.countable) {
+              marker.index -= this.length
+            }
+          }
+        })
+      }
+      if (right.keep) {
+        this.keep = true
+      }
+      this.right = right.right
+      if (this.right !== null) {
+        this.right.left = this
+      }
+      this.length += right.length
+      return true
+    }
+    return false
+  }
+
+  /**
+   * Mark this Item as deleted.
+   *
+   * @param {Transaction} transaction
+   */
+  delete (transaction) {
+    if (!this.deleted) {
+      const parent = /** @type {AbstractType<any>} */ (this.parent)
+      // adjust the length of parent
+      if (this.countable && this.parentSub === null) {
+        parent._length -= this.length
+      }
+      this.markDeleted()
+      addToDeleteSet(transaction.deleteSet, this.id.client, this.id.clock, this.length)
+      addChangedTypeToTransaction(transaction, parent, this.parentSub)
+      this.content.delete(transaction)
+    }
+  }
+
+  /**
+   * @param {StructStore} store
+   * @param {boolean} parentGCd
+   */
+  gc (store, parentGCd) {
+    if (!this.deleted) {
+      throw error.unexpectedCase()
+    }
+    this.content.gc(store)
+    if (parentGCd) {
+      replaceStruct(store, this, new GC(this.id, this.length))
+    } else {
+      this.content = new ContentDeleted(this.length)
+    }
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    const origin = offset > 0 ? createID(this.id.client, this.id.clock + offset - 1) : this.origin
+    const rightOrigin = this.rightOrigin
+    const parentSub = this.parentSub
+    const info = (this.content.getRef() & binary.BITS5) |
+      (origin === null ? 0 : binary.BIT8) | // origin is defined
+      (rightOrigin === null ? 0 : binary.BIT7) | // right origin is defined
+      (parentSub === null ? 0 : binary.BIT6) // parentSub is non-null
+    encoder.writeInfo(info)
+    if (origin !== null) {
+      encoder.writeLeftID(origin)
+    }
+    if (rightOrigin !== null) {
+      encoder.writeRightID(rightOrigin)
+    }
+    if (origin === null && rightOrigin === null) {
+      const parent = /** @type {AbstractType<any>} */ (this.parent)
+      if (parent._item !== undefined) {
+        const parentItem = parent._item
+        if (parentItem === null) {
+          // parent type on y._map
+          // find the correct key
+          const ykey = findRootTypeKey(parent)
+          encoder.writeParentInfo(true) // write parentYKey
+          encoder.writeString(ykey)
+        } else {
+          encoder.writeParentInfo(false) // write parent id
+          encoder.writeLeftID(parentItem.id)
+        }
+      } else if (parent.constructor === String) { // this edge case was added by differential updates
+        encoder.writeParentInfo(true) // write parentYKey
+        encoder.writeString(parent)
+      } else if (parent.constructor === ID) {
+        encoder.writeParentInfo(false) // write parent id
+        encoder.writeLeftID(parent)
+      } else {
+        error.unexpectedCase()
+      }
+      if (parentSub !== null) {
+        encoder.writeString(parentSub)
+      }
+    }
+    this.content.write(encoder, offset)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @param {number} info
+ */
+export const readItemContent = (decoder, info) => contentRefs[info & binary.BITS5](decoder)
+
+/**
+ * A lookup map for reading Item content.
+ *
+ * @type {Array<function(UpdateDecoderV1 | UpdateDecoderV2):AbstractContent>}
+ */
+export const contentRefs = [
+  () => { error.unexpectedCase() }, // GC is not ItemContent
+  readContentDeleted, // 1
+  readContentJSON, // 2
+  readContentBinary, // 3
+  readContentString, // 4
+  readContentEmbed, // 5
+  readContentFormat, // 6
+  readContentType, // 7
+  readContentAny, // 8
+  readContentDoc, // 9
+  () => { error.unexpectedCase() } // 10 - Skip is not ItemContent
+]
+
+/**
+ * Do not implement this class!
+ */
+export class AbstractContent {
+  /**
+   * @return {number}
+   */
+  getLength () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {Array<any>}
+   */
+  getContent () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * Should return false if this Item is some kind of meta information
+   * (e.g. format information).
+   *
+   * * Whether this Item should be addressable via `yarray.get(i)`
+   * * Whether this Item should be counted when computing yarray.length
+   *
+   * @return {boolean}
+   */
+  isCountable () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {AbstractContent}
+   */
+  copy () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {number} _offset
+   * @return {AbstractContent}
+   */
+  splice (_offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {AbstractContent} _right
+   * @return {boolean}
+   */
+  mergeWith (_right) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} _transaction
+   * @param {Item} _item
+   */
+  integrate (_transaction, _item) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {Transaction} _transaction
+   */
+  delete (_transaction) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {StructStore} _store
+   */
+  gc (_store) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} _encoder
+   * @param {number} _offset
+   */
+  write (_encoder, _offset) {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @return {number}
+   */
+  getRef () {
+    throw error.methodUnimplemented()
+  }
+}
--- a/src/structs/Skip.js
+++ b/src/structs/Skip.js
@ -0,0 +1,59 @@
+import {
+  AbstractStruct,
+  UpdateEncoderV1, UpdateEncoderV2, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+import * as error from 'lib0/error'
+import * as encoding from 'lib0/encoding'
+
+export const structSkipRefNumber = 10
+
+/**
+ * @private
+ */
+export class Skip extends AbstractStruct {
+  get deleted () {
+    return true
+  }
+
+  delete () {}
+
+  /**
+   * @param {Skip} right
+   * @return {boolean}
+   */
+  mergeWith (right) {
+    if (this.constructor !== right.constructor) {
+      return false
+    }
+    this.length += right.length
+    return true
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {number} offset
+   */
+  integrate (transaction, offset) {
+    // skip structs cannot be integrated
+    error.unexpectedCase()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   * @param {number} offset
+   */
+  write (encoder, offset) {
+    encoder.writeInfo(structSkipRefNumber)
+    // write as VarUint because Skips can't make use of predictable length-encoding
+    encoding.writeVarUint(encoder.restEncoder, this.length - offset)
+  }
+
+  /**
+   * @param {Transaction} transaction
+   * @param {StructStore} store
+   * @return {null | number}
+   */
+  getMissing (transaction, store) {
+    return null
+  }
+}
--- a/src/types/AbstractType.js
+++ b/src/types/AbstractType.js
@ -0,0 +1,983 @@
+import {
+  removeEventHandlerListener,
+  callEventHandlerListeners,
+  addEventHandlerListener,
+  createEventHandler,
+  getState,
+  isVisible,
+  ContentType,
+  createID,
+  ContentAny,
+  ContentBinary,
+  getItemCleanStart,
+  ContentDoc, YText, YArray, UpdateEncoderV1, UpdateEncoderV2, Doc, Snapshot, Transaction, EventHandler, YEvent, Item, // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as iterator from 'lib0/iterator'
+import * as error from 'lib0/error'
+import * as math from 'lib0/math'
+import * as log from 'lib0/logging'
+
+/**
+ * https://docs.yjs.dev/getting-started/working-with-shared-types#caveats
+ */
+export const warnPrematureAccess = () => { log.warn('Invalid access: Add Yjs type to a document before reading data.') }
+
+const maxSearchMarker = 80
+
+/**
+ * A unique timestamp that identifies each marker.
+ *
+ * Time is relative,.. this is more like an ever-increasing clock.
+ *
+ * @type {number}
+ */
+let globalSearchMarkerTimestamp = 0
+
+export class ArraySearchMarker {
+  /**
+   * @param {Item} p
+   * @param {number} index
+   */
+  constructor (p, index) {
+    p.marker = true
+    this.p = p
+    this.index = index
+    this.timestamp = globalSearchMarkerTimestamp++
+  }
+}
+
+/**
+ * @param {ArraySearchMarker} marker
+ */
+const refreshMarkerTimestamp = marker => { marker.timestamp = globalSearchMarkerTimestamp++ }
+
+/**
+ * This is rather complex so this function is the only thing that should overwrite a marker
+ *
+ * @param {ArraySearchMarker} marker
+ * @param {Item} p
+ * @param {number} index
+ */
+const overwriteMarker = (marker, p, index) => {
+  marker.p.marker = false
+  marker.p = p
+  p.marker = true
+  marker.index = index
+  marker.timestamp = globalSearchMarkerTimestamp++
+}
+
+/**
+ * @param {Array<ArraySearchMarker>} searchMarker
+ * @param {Item} p
+ * @param {number} index
+ */
+const markPosition = (searchMarker, p, index) => {
+  if (searchMarker.length >= maxSearchMarker) {
+    // override oldest marker (we don't want to create more objects)
+    const marker = searchMarker.reduce((a, b) => a.timestamp < b.timestamp ? a : b)
+    overwriteMarker(marker, p, index)
+    return marker
+  } else {
+    // create new marker
+    const pm = new ArraySearchMarker(p, index)
+    searchMarker.push(pm)
+    return pm
+  }
+}
+
+/**
+ * Search marker help us to find positions in the associative array faster.
+ *
+ * They speed up the process of finding a position without much bookkeeping.
+ *
+ * A maximum of `maxSearchMarker` objects are created.
+ *
+ * This function always returns a refreshed marker (updated timestamp)
+ *
+ * @param {AbstractType<any>} yarray
+ * @param {number} index
+ */
+export const findMarker = (yarray, index) => {
+  if (yarray._start === null || index === 0 || yarray._searchMarker === null) {
+    return null
+  }
+  const marker = yarray._searchMarker.length === 0 ? null : yarray._searchMarker.reduce((a, b) => math.abs(index - a.index) < math.abs(index - b.index) ? a : b)
+  let p = yarray._start
+  let pindex = 0
+  if (marker !== null) {
+    p = marker.p
+    pindex = marker.index
+    refreshMarkerTimestamp(marker) // we used it, we might need to use it again
+  }
+  // iterate to right if possible
+  while (p.right !== null && pindex < index) {
+    if (!p.deleted && p.countable) {
+      if (index < pindex + p.length) {
+        break
+      }
+      pindex += p.length
+    }
+    p = p.right
+  }
+  // iterate to left if necessary (might be that pindex > index)
+  while (p.left !== null && pindex > index) {
+    p = p.left
+    if (!p.deleted && p.countable) {
+      pindex -= p.length
+    }
+  }
+  // we want to make sure that p can't be merged with left, because that would screw up everything
+  // in that cas just return what we have (it is most likely the best marker anyway)
+  // iterate to left until p can't be merged with left
+  while (p.left !== null && p.left.id.client === p.id.client && p.left.id.clock + p.left.length === p.id.clock) {
+    p = p.left
+    if (!p.deleted && p.countable) {
+      pindex -= p.length
+    }
+  }
+
+  // @todo remove!
+  // assure position
+  // {
+  //   let start = yarray._start
+  //   let pos = 0
+  //   while (start !== p) {
+  //     if (!start.deleted && start.countable) {
+  //       pos += start.length
+  //     }
+  //     start = /** @type {Item} */ (start.right)
+  //   }
+  //   if (pos !== pindex) {
+  //     debugger
+  //     throw new Error('Gotcha position fail!')
+  //   }
+  // }
+  // if (marker) {
+  //   if (window.lengths == null) {
+  //     window.lengths = []
+  //     window.getLengths = () => window.lengths.sort((a, b) => a - b)
+  //   }
+  //   window.lengths.push(marker.index - pindex)
+  //   console.log('distance', marker.index - pindex, 'len', p && p.parent.length)
+  // }
+  if (marker !== null && math.abs(marker.index - pindex) < /** @type {YText|YArray<any>} */ (p.parent).length / maxSearchMarker) {
+    // adjust existing marker
+    overwriteMarker(marker, p, pindex)
+    return marker
+  } else {
+    // create new marker
+    return markPosition(yarray._searchMarker, p, pindex)
+  }
+}
+
+/**
+ * Update markers when a change happened.
+ *
+ * This should be called before doing a deletion!
+ *
+ * @param {Array<ArraySearchMarker>} searchMarker
+ * @param {number} index
+ * @param {number} len If insertion, len is positive. If deletion, len is negative.
+ */
+export const updateMarkerChanges = (searchMarker, index, len) => {
+  for (let i = searchMarker.length - 1; i >= 0; i--) {
+    const m = searchMarker[i]
+    if (len > 0) {
+      /**
+       * @type {Item|null}
+       */
+      let p = m.p
+      p.marker = false
+      // Ideally we just want to do a simple position comparison, but this will only work if
+      // search markers don't point to deleted items for formats.
+      // Iterate marker to prev undeleted countable position so we know what to do when updating a position
+      while (p && (p.deleted || !p.countable)) {
+        p = p.left
+        if (p && !p.deleted && p.countable) {
+          // adjust position. the loop should break now
+          m.index -= p.length
+        }
+      }
+      if (p === null || p.marker === true) {
+        // remove search marker if updated position is null or if position is already marked
+        searchMarker.splice(i, 1)
+        continue
+      }
+      m.p = p
+      p.marker = true
+    }
+    if (index < m.index || (len > 0 && index === m.index)) { // a simple index <= m.index check would actually suffice
+      m.index = math.max(index, m.index + len)
+    }
+  }
+}
+
+/**
+ * Accumulate all (list) children of a type and return them as an Array.
+ *
+ * @param {AbstractType<any>} t
+ * @return {Array<Item>}
+ */
+export const getTypeChildren = t => {
+  t.doc ?? warnPrematureAccess()
+  let s = t._start
+  const arr = []
+  while (s) {
+    arr.push(s)
+    s = s.right
+  }
+  return arr
+}
+
+/**
+ * Call event listeners with an event. This will also add an event to all
+ * parents (for `.observeDeep` handlers).
+ *
+ * @template EventType
+ * @param {AbstractType<EventType>} type
+ * @param {Transaction} transaction
+ * @param {EventType} event
+ */
+export const callTypeObservers = (type, transaction, event) => {
+  const changedType = type
+  const changedParentTypes = transaction.changedParentTypes
+  while (true) {
+    // @ts-ignore
+    map.setIfUndefined(changedParentTypes, type, () => []).push(event)
+    if (type._item === null) {
+      break
+    }
+    type = /** @type {AbstractType<any>} */ (type._item.parent)
+  }
+  callEventHandlerListeners(changedType._eH, event, transaction)
+}
+
+/**
+ * @template EventType
+ * Abstract Yjs Type class
+ */
+export class AbstractType {
+  constructor () {
+    /**
+     * @type {Item|null}
+     */
+    this._item = null
+    /**
+     * @type {Map<string,Item>}
+     */
+    this._map = new Map()
+    /**
+     * @type {Item|null}
+     */
+    this._start = null
+    /**
+     * @type {Doc|null}
+     */
+    this.doc = null
+    this._length = 0
+    /**
+     * Event handlers
+     * @type {EventHandler<EventType,Transaction>}
+     */
+    this._eH = createEventHandler()
+    /**
+     * Deep event handlers
+     * @type {EventHandler<Array<YEvent<any>>,Transaction>}
+     */
+    this._dEH = createEventHandler()
+    /**
+     * @type {null | Array<ArraySearchMarker>}
+     */
+    this._searchMarker = null
+  }
+
+  /**
+   * @return {AbstractType<any>|null}
+   */
+  get parent () {
+    return this._item ? /** @type {AbstractType<any>} */ (this._item.parent) : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item|null} item
+   */
+  _integrate (y, item) {
+    this.doc = y
+    this._item = item
+  }
+
+  /**
+   * @return {AbstractType<EventType>}
+   */
+  _copy () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {AbstractType<EventType>}
+   */
+  clone () {
+    throw error.methodUnimplemented()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} _encoder
+   */
+  _write (_encoder) { }
+
+  /**
+   * The first non-deleted item
+   */
+  get _first () {
+    let n = this._start
+    while (n !== null && n.deleted) {
+      n = n.right
+    }
+    return n
+  }
+
+  /**
+   * Creates YEvent and calls all type observers.
+   * Must be implemented by each type.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} _parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, _parentSubs) {
+    if (!transaction.local && this._searchMarker) {
+      this._searchMarker.length = 0
+    }
+  }
+
+  /**
+   * Observe all events that are created on this type.
+   *
+   * @param {function(EventType, Transaction):void} f Observer function
+   */
+  observe (f) {
+    addEventHandlerListener(this._eH, f)
+  }
+
+  /**
+   * Observe all events that are created by this type and its children.
+   *
+   * @param {function(Array<YEvent<any>>,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<any>>,Transaction):void} f Observer function
+   */
+  unobserveDeep (f) {
+    removeEventHandlerListener(this._dEH, f)
+  }
+
+  /**
+   * @abstract
+   * @return {any}
+   */
+  toJSON () {}
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} start
+ * @param {number} end
+ * @return {Array<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListSlice = (type, start, end) => {
+  type.doc ?? warnPrematureAccess()
+  if (start < 0) {
+    start = type._length + start
+  }
+  if (end < 0) {
+    end = type._length + end
+  }
+  let len = end - start
+  const cs = []
+  let n = type._start
+  while (n !== null && len > 0) {
+    if (n.countable && !n.deleted) {
+      const c = n.content.getContent()
+      if (c.length <= start) {
+        start -= c.length
+      } else {
+        for (let i = start; i < c.length && len > 0; i++) {
+          cs.push(c[i])
+          len--
+        }
+        start = 0
+      }
+    }
+    n = n.right
+  }
+  return cs
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @return {Array<any>}
+ *
+ * @private
+ * @function
+ */
+export const typeListToArray = type => {
+  type.doc ?? warnPrematureAccess()
+  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 every 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
+  type.doc ?? warnPrematureAccess()
+  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 every 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) => {
+  type.doc ?? warnPrematureAccess()
+  const marker = findMarker(type, index)
+  let n = type._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+  }
+  for (; n !== null; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index < n.length) {
+        return n.content.getContent()[index]
+      }
+      index -= n.length
+    }
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Item?} referenceItem
+ * @param {Array<Object<string,any>|Array<any>|boolean|number|null|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenericsAfter = (transaction, parent, referenceItem, content) => {
+  let left = referenceItem
+  const doc = transaction.doc
+  const ownClientId = doc.clientID
+  const store = doc.store
+  const right = referenceItem === null ? parent._start : referenceItem.right
+  /**
+   * @type {Array<Object|Array<any>|number|null>}
+   */
+  let jsonContent = []
+  const packJsonContent = () => {
+    if (jsonContent.length > 0) {
+      left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentAny(jsonContent))
+      left.integrate(transaction, 0)
+      jsonContent = []
+    }
+  }
+  content.forEach(c => {
+    if (c === null) {
+      jsonContent.push(c)
+    } else {
+      switch (c.constructor) {
+        case Number:
+        case Object:
+        case Boolean:
+        case Array:
+        case String:
+          jsonContent.push(c)
+          break
+        default:
+          packJsonContent()
+          switch (c.constructor) {
+            case Uint8Array:
+            case ArrayBuffer:
+              left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentBinary(new Uint8Array(/** @type {Uint8Array} */ (c))))
+              left.integrate(transaction, 0)
+              break
+            case Doc:
+              left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentDoc(/** @type {Doc} */ (c)))
+              left.integrate(transaction, 0)
+              break
+            default:
+              if (c instanceof AbstractType) {
+                left = new Item(createID(ownClientId, getState(store, ownClientId)), left, left && left.lastId, right, right && right.id, parent, null, new ContentType(c))
+                left.integrate(transaction, 0)
+              } else {
+                throw new Error('Unexpected content type in insert operation')
+              }
+          }
+      }
+    }
+  })
+  packJsonContent()
+}
+
+const lengthExceeded = () => error.create('Length exceeded!')
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @param {Array<Object<string,any>|Array<any>|number|null|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListInsertGenerics = (transaction, parent, index, content) => {
+  if (index > parent._length) {
+    throw lengthExceeded()
+  }
+  if (index === 0) {
+    if (parent._searchMarker) {
+      updateMarkerChanges(parent._searchMarker, index, content.length)
+    }
+    return typeListInsertGenericsAfter(transaction, parent, null, content)
+  }
+  const startIndex = index
+  const marker = findMarker(parent, index)
+  let n = parent._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+    // we need to iterate one to the left so that the algorithm works
+    if (index === 0) {
+      // @todo refactor this as it actually doesn't consider formats
+      n = n.prev // important! get the left undeleted item so that we can actually decrease index
+      index += (n && n.countable && !n.deleted) ? n.length : 0
+    }
+  }
+  for (; n !== null; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index <= n.length) {
+        if (index < n.length) {
+          // insert in-between
+          getItemCleanStart(transaction, createID(n.id.client, n.id.clock + index))
+        }
+        break
+      }
+      index -= n.length
+    }
+  }
+  if (parent._searchMarker) {
+    updateMarkerChanges(parent._searchMarker, startIndex, content.length)
+  }
+  return typeListInsertGenericsAfter(transaction, parent, n, content)
+}
+
+/**
+ * Pushing content is special as we generally want to push after the last item. So we don't have to update
+ * the search marker.
+ *
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {Array<Object<string,any>|Array<any>|number|null|string|Uint8Array>} content
+ *
+ * @private
+ * @function
+ */
+export const typeListPushGenerics = (transaction, parent, content) => {
+  // Use the marker with the highest index and iterate to the right.
+  const marker = (parent._searchMarker || []).reduce((maxMarker, currMarker) => currMarker.index > maxMarker.index ? currMarker : maxMarker, { index: 0, p: parent._start })
+  let n = marker.p
+  if (n) {
+    while (n.right) {
+      n = n.right
+    }
+  }
+  return typeListInsertGenericsAfter(transaction, parent, n, content)
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {number} index
+ * @param {number} length
+ *
+ * @private
+ * @function
+ */
+export const typeListDelete = (transaction, parent, index, length) => {
+  if (length === 0) { return }
+  const startIndex = index
+  const startLength = length
+  const marker = findMarker(parent, index)
+  let n = parent._start
+  if (marker !== null) {
+    n = marker.p
+    index -= marker.index
+  }
+  // compute the first item to be deleted
+  for (; n !== null && index > 0; n = n.right) {
+    if (!n.deleted && n.countable) {
+      if (index < n.length) {
+        getItemCleanStart(transaction, createID(n.id.client, n.id.clock + index))
+      }
+      index -= n.length
+    }
+  }
+  // delete all items until done
+  while (length > 0 && n !== null) {
+    if (!n.deleted) {
+      if (length < n.length) {
+        getItemCleanStart(transaction, createID(n.id.client, n.id.clock + length))
+      }
+      n.delete(transaction)
+      length -= n.length
+    }
+    n = n.right
+  }
+  if (length > 0) {
+    throw lengthExceeded()
+  }
+  if (parent._searchMarker) {
+    updateMarkerChanges(parent._searchMarker, startIndex, -startLength + length /* in case we remove the above exception */)
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ *
+ * @private
+ * @function
+ */
+export const typeMapDelete = (transaction, parent, key) => {
+  const c = parent._map.get(key)
+  if (c !== undefined) {
+    c.delete(transaction)
+  }
+}
+
+/**
+ * @param {Transaction} transaction
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @param {Object|number|null|Array<any>|string|Uint8Array|AbstractType<any>} value
+ *
+ * @private
+ * @function
+ */
+export const typeMapSet = (transaction, parent, key, value) => {
+  const left = parent._map.get(key) || null
+  const doc = transaction.doc
+  const ownClientId = doc.clientID
+  let content
+  if (value == null) {
+    content = new ContentAny([value])
+  } else {
+    switch (value.constructor) {
+      case Number:
+      case Object:
+      case Boolean:
+      case Array:
+      case String:
+        content = new ContentAny([value])
+        break
+      case Uint8Array:
+        content = new ContentBinary(/** @type {Uint8Array} */ (value))
+        break
+      case Doc:
+        content = new ContentDoc(/** @type {Doc} */ (value))
+        break
+      default:
+        if (value instanceof AbstractType) {
+          content = new ContentType(value)
+        } else {
+          throw new Error('Unexpected content type')
+        }
+    }
+  }
+  new Item(createID(ownClientId, getState(doc.store, ownClientId)), left, left && left.lastId, null, null, parent, key, content).integrate(transaction, 0)
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @return {Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGet = (parent, key) => {
+  parent.doc ?? warnPrematureAccess()
+  const val = parent._map.get(key)
+  return val !== undefined && !val.deleted ? val.content.getContent()[val.length - 1] : undefined
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @return {Object<string,Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined>}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetAll = (parent) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const res = {}
+  parent.doc ?? warnPrematureAccess()
+  parent._map.forEach((value, key) => {
+    if (!value.deleted) {
+      res[key] = value.content.getContent()[value.length - 1]
+    }
+  })
+  return res
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @return {boolean}
+ *
+ * @private
+ * @function
+ */
+export const typeMapHas = (parent, key) => {
+  parent.doc ?? warnPrematureAccess()
+  const val = parent._map.get(key)
+  return val !== undefined && !val.deleted
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {string} key
+ * @param {Snapshot} snapshot
+ * @return {Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetSnapshot = (parent, key, snapshot) => {
+  let v = parent._map.get(key) || null
+  while (v !== null && (!snapshot.sv.has(v.id.client) || v.id.clock >= (snapshot.sv.get(v.id.client) || 0))) {
+    v = v.left
+  }
+  return v !== null && isVisible(v, snapshot) ? v.content.getContent()[v.length - 1] : undefined
+}
+
+/**
+ * @param {AbstractType<any>} parent
+ * @param {Snapshot} snapshot
+ * @return {Object<string,Object<string,any>|number|null|Array<any>|string|Uint8Array|AbstractType<any>|undefined>}
+ *
+ * @private
+ * @function
+ */
+export const typeMapGetAllSnapshot = (parent, snapshot) => {
+  /**
+   * @type {Object<string,any>}
+   */
+  const res = {}
+  parent._map.forEach((value, key) => {
+    /**
+     * @type {Item|null}
+     */
+    let v = value
+    while (v !== null && (!snapshot.sv.has(v.id.client) || v.id.clock >= (snapshot.sv.get(v.id.client) || 0))) {
+      v = v.left
+    }
+    if (v !== null && isVisible(v, snapshot)) {
+      res[key] = v.content.getContent()[v.length - 1]
+    }
+  })
+  return res
+}
+
+/**
+ * @param {AbstractType<any> & { _map: Map<string, Item> }} type
+ * @return {IterableIterator<Array<any>>}
+ *
+ * @private
+ * @function
+ */
+export const createMapIterator = type => {
+  type.doc ?? warnPrematureAccess()
+  return iterator.iteratorFilter(type._map.entries(), /** @param {any} entry */ entry => !entry[1].deleted)
+}
--- a/src/types/YArray.js
+++ b/src/types/YArray.js
@ -0,0 +1,274 @@
+/**
+ * @module YArray
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeListGet,
+  typeListToArray,
+  typeListForEach,
+  typeListCreateIterator,
+  typeListInsertGenerics,
+  typeListPushGenerics,
+  typeListDelete,
+  typeListMap,
+  YArrayRefID,
+  callTypeObservers,
+  transact,
+  warnPrematureAccess,
+  ArraySearchMarker, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+import { typeListSlice } from './AbstractType.js'
+
+/**
+ * Event that describes the changes on a YArray
+ * @template T
+ * @extends YEvent<YArray<T>>
+ */
+export class YArrayEvent extends YEvent {}
+
+/**
+ * A shared Array implementation.
+ * @template T
+ * @extends AbstractType<YArrayEvent<T>>
+ * @implements {Iterable<T>}
+ */
+export class YArray extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Array<any>?}
+     * @private
+     */
+    this._prelimContent = []
+    /**
+     * @type {Array<ArraySearchMarker>}
+     */
+    this._searchMarker = []
+  }
+
+  /**
+   * Construct a new YArray containing the specified items.
+   * @template {Object<string,any>|Array<any>|number|null|string|Uint8Array} T
+   * @param {Array<T>} items
+   * @return {YArray<T>}
+   */
+  static from (items) {
+    /**
+     * @type {YArray<T>}
+     */
+    const a = new YArray()
+    a.push(items)
+    return a
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    this.insert(0, /** @type {Array<any>} */ (this._prelimContent))
+    this._prelimContent = null
+  }
+
+  /**
+   * @return {YArray<T>}
+   */
+  _copy () {
+    return new YArray()
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YArray<T>}
+   */
+  clone () {
+    /**
+     * @type {YArray<T>}
+     */
+    const arr = new YArray()
+    arr.insert(0, this.toArray().map(el =>
+      el instanceof AbstractType ? /** @type {typeof el} */ (el.clone()) : el
+    ))
+    return arr
+  }
+
+  get length () {
+    this.doc ?? warnPrematureAccess()
+    return this._length
+  }
+
+  /**
+   * Creates YArrayEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    super._callObserver(transaction, parentSubs)
+    callTypeObservers(this, transaction, new YArrayEvent(this, transaction))
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * Important: This function expects an array of content. Not just a content
+   * object. The reason for this "weirdness" is that inserting several elements
+   * is very efficient when it is done as a single operation.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  yarray.insert(0, ['a'])
+   *  // Insert numbers 1, 2 at position 1
+   *  yarray.insert(1, [1, 2])
+   *
+   * @param {number} index The index to insert content at.
+   * @param {Array<T>} content The array of content
+   */
+  insert (index, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListInsertGenerics(transaction, this, index, /** @type {any} */ (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.
+   *
+   * @todo Use the following implementation in all types.
+   */
+  push (content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListPushGenerics(transaction, this, /** @type {any} */ (content))
+      })
+    } else {
+      /** @type {Array<any>} */ (this._prelimContent).push(...content)
+    }
+  }
+
+  /**
+   * Prepends content to this YArray.
+   *
+   * @param {Array<T>} content Array of content to prepend.
+   */
+  unshift (content) {
+    this.insert(0, content)
+  }
+
+  /**
+   * Deletes elements starting from an index.
+   *
+   * @param {number} index Index at which to start deleting elements
+   * @param {number} length The number of elements to remove. Defaults to 1.
+   */
+  delete (index, length = 1) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListDelete(transaction, this, index, length)
+      })
+    } else {
+      /** @type {Array<any>} */ (this._prelimContent).splice(index, length)
+    }
+  }
+
+  /**
+   * Returns the i-th element from a YArray.
+   *
+   * @param {number} index The index of the element to return from the YArray
+   * @return {T}
+   */
+  get (index) {
+    return typeListGet(this, index)
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @return {Array<T>}
+   */
+  toArray () {
+    return typeListToArray(this)
+  }
+
+  /**
+   * Returns a portion of this YArray into a JavaScript Array selected
+   * from start to end (end not included).
+   *
+   * @param {number} [start]
+   * @param {number} [end]
+   * @return {Array<T>}
+   */
+  slice (start = 0, end = this.length) {
+    return typeListSlice(this, start, end)
+  }
+
+  /**
+   * Transforms this Shared Type to a JSON object.
+   *
+   * @return {Array<any>}
+   */
+  toJSON () {
+    return this.map(c => c instanceof AbstractType ? c.toJSON() : c)
+  }
+
+  /**
+   * Returns an Array with the result of calling a provided function on every
+   * element of this YArray.
+   *
+   * @template M
+   * @param {function(T,number,YArray<T>):M} f Function that produces an element of the new Array
+   * @return {Array<M>} A new array with each element being the result of the
+   *                 callback function
+   */
+  map (f) {
+    return typeListMap(this, /** @type {any} */ (f))
+  }
+
+  /**
+   * Executes a provided function once on every element of this YArray.
+   *
+   * @param {function(T,number,YArray<T>):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    typeListForEach(this, f)
+  }
+
+  /**
+   * @return {IterableIterator<T>}
+   */
+  [Symbol.iterator] () {
+    return typeListCreateIterator(this)
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YArrayRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} _decoder
+ *
+ * @private
+ * @function
+ */
+export const readYArray = _decoder => new YArray()
--- a/src/types/YMap.js
+++ b/src/types/YMap.js
@ -0,0 +1,281 @@
+/**
+ * @module YMap
+ */
+
+import {
+  YEvent,
+  AbstractType,
+  typeMapDelete,
+  typeMapSet,
+  typeMapGet,
+  typeMapHas,
+  createMapIterator,
+  YMapRefID,
+  callTypeObservers,
+  transact,
+  warnPrematureAccess,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, Transaction, Item // eslint-disable-line
+} from '../internals.js'
+
+import * as iterator from 'lib0/iterator'
+
+/**
+ * @template T
+ * @extends YEvent<YMap<T>>
+ * Event that describes the changes on a YMap.
+ */
+export class YMapEvent extends YEvent {
+  /**
+   * @param {YMap<T>} ymap The YArray that changed.
+   * @param {Transaction} transaction
+   * @param {Set<any>} subs The keys that changed.
+   */
+  constructor (ymap, transaction, subs) {
+    super(ymap, transaction)
+    this.keysChanged = subs
+  }
+}
+
+/**
+ * @template MapType
+ * A shared Map implementation.
+ *
+ * @extends AbstractType<YMapEvent<MapType>>
+ * @implements {Iterable<[string, MapType]>}
+ */
+export class YMap extends AbstractType {
+  /**
+   *
+   * @param {Iterable<readonly [string, any]>=} entries - an optional iterable to initialize the YMap
+   */
+  constructor (entries) {
+    super()
+    /**
+     * @type {Map<string,any>?}
+     * @private
+     */
+    this._prelimContent = null
+
+    if (entries === undefined) {
+      this._prelimContent = new Map()
+    } else {
+      this._prelimContent = new Map(entries)
+    }
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    ;/** @type {Map<string, any>} */ (this._prelimContent).forEach((value, key) => {
+      this.set(key, value)
+    })
+    this._prelimContent = null
+  }
+
+  /**
+   * @return {YMap<MapType>}
+   */
+  _copy () {
+    return new YMap()
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YMap<MapType>}
+   */
+  clone () {
+    /**
+     * @type {YMap<MapType>}
+     */
+    const map = new YMap()
+    this.forEach((value, key) => {
+      map.set(key, value instanceof AbstractType ? /** @type {typeof value} */ (value.clone()) : value)
+    })
+    return map
+  }
+
+  /**
+   * Creates YMapEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    callTypeObservers(this, transaction, new YMapEvent(this, transaction, parentSubs))
+  }
+
+  /**
+   * Transforms this Shared Type to a JSON object.
+   *
+   * @return {Object<string,any>}
+   */
+  toJSON () {
+    this.doc ?? warnPrematureAccess()
+    /**
+     * @type {Object<string,MapType>}
+     */
+    const map = {}
+    this._map.forEach((item, key) => {
+      if (!item.deleted) {
+        const v = item.content.getContent()[item.length - 1]
+        map[key] = v instanceof AbstractType ? v.toJSON() : v
+      }
+    })
+    return map
+  }
+
+  /**
+   * Returns the size of the YMap (count of key/value pairs)
+   *
+   * @return {number}
+   */
+  get size () {
+    return [...createMapIterator(this)].length
+  }
+
+  /**
+   * Returns the keys for each element in the YMap Type.
+   *
+   * @return {IterableIterator<string>}
+   */
+  keys () {
+    return iterator.iteratorMap(createMapIterator(this), /** @param {any} v */ v => v[0])
+  }
+
+  /**
+   * Returns the values for each element in the YMap Type.
+   *
+   * @return {IterableIterator<MapType>}
+   */
+  values () {
+    return iterator.iteratorMap(createMapIterator(this), /** @param {any} v */ v => v[1].content.getContent()[v[1].length - 1])
+  }
+
+  /**
+   * Returns an Iterator of [key, value] pairs
+   *
+   * @return {IterableIterator<[string, MapType]>}
+   */
+  entries () {
+    return iterator.iteratorMap(createMapIterator(this), /** @param {any} v */ v => /** @type {any} */ ([v[0], v[1].content.getContent()[v[1].length - 1]]))
+  }
+
+  /**
+   * Executes a provided function on once on every key-value pair.
+   *
+   * @param {function(MapType,string,YMap<MapType>):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    this.doc ?? warnPrematureAccess()
+    this._map.forEach((item, key) => {
+      if (!item.deleted) {
+        f(item.content.getContent()[item.length - 1], key, this)
+      }
+    })
+  }
+
+  /**
+   * Returns an Iterator of [key, value] pairs
+   *
+   * @return {IterableIterator<[string, MapType]>}
+   */
+  [Symbol.iterator] () {
+    return this.entries()
+  }
+
+  /**
+   * Remove a specified element from this YMap.
+   *
+   * @param {string} key The key of the element to remove.
+   */
+  delete (key) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapDelete(transaction, this, key)
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).delete(key)
+    }
+  }
+
+  /**
+   * Adds or updates an element with a specified key and value.
+   * @template {MapType} VAL
+   *
+   * @param {string} key The key of the element to add to this YMap
+   * @param {VAL} value The value of the element to add
+   * @return {VAL}
+   */
+  set (key, value) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapSet(transaction, this, key, /** @type {any} */ (value))
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).set(key, value)
+    }
+    return value
+  }
+
+  /**
+   * Returns a specified element from this YMap.
+   *
+   * @param {string} key
+   * @return {MapType|undefined}
+   */
+  get (key) {
+    return /** @type {any} */ (typeMapGet(this, key))
+  }
+
+  /**
+   * Returns a boolean indicating whether the specified key exists or not.
+   *
+   * @param {string} key The key to test.
+   * @return {boolean}
+   */
+  has (key) {
+    return typeMapHas(this, key)
+  }
+
+  /**
+   * Removes all elements from this YMap.
+   */
+  clear () {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        this.forEach(function (_value, key, map) {
+          typeMapDelete(transaction, map, key)
+        })
+      })
+    } else {
+      /** @type {Map<string, any>} */ (this._prelimContent).clear()
+    }
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YMapRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} _decoder
+ *
+ * @private
+ * @function
+ */
+export const readYMap = _decoder => new YMap()
--- a/src/types/YText.js
+++ b/src/types/YText.js
--- a/src/types/YXmlElement.js
+++ b/src/types/YXmlElement.js
@ -0,0 +1,262 @@
+import * as object from 'lib0/object'
+
+import {
+  YXmlFragment,
+  transact,
+  typeMapDelete,
+  typeMapHas,
+  typeMapSet,
+  typeMapGet,
+  typeMapGetAll,
+  typeMapGetAllSnapshot,
+  typeListForEach,
+  YXmlElementRefID,
+  Snapshot, YXmlText, ContentType, AbstractType, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, Item // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @typedef {Object|number|null|Array<any>|string|Uint8Array|AbstractType<any>} ValueTypes
+ */
+
+/**
+ * An YXmlElement imitates the behavior of a
+ * 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
+ *
+ * @template {{ [key: string]: ValueTypes }} [KV={ [key: string]: string }]
+ */
+export class YXmlElement extends YXmlFragment {
+  constructor (nodeName = 'UNDEFINED') {
+    super()
+    this.nodeName = nodeName
+    /**
+     * @type {Map<string, any>|null}
+     */
+    this._prelimAttrs = new Map()
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get nextSibling () {
+    const n = this._item ? this._item.next : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get prevSibling () {
+    const n = this._item ? this._item.prev : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    ;(/** @type {Map<string, any>} */ (this._prelimAttrs)).forEach((value, key) => {
+      this.setAttribute(key, value)
+    })
+    this._prelimAttrs = null
+  }
+
+  /**
+   * Creates an Item with the same effect as this Item (without position effect)
+   *
+   * @return {YXmlElement}
+   */
+  _copy () {
+    return new YXmlElement(this.nodeName)
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YXmlElement<KV>}
+   */
+  clone () {
+    /**
+     * @type {YXmlElement<KV>}
+     */
+    const el = new YXmlElement(this.nodeName)
+    const attrs = this.getAttributes()
+    object.forEach(attrs, (value, key) => {
+      if (typeof value === 'string') {
+        el.setAttribute(key, value)
+      }
+    })
+    // @ts-ignore
+    el.insert(0, this.toArray().map(item => item instanceof AbstractType ? item.clone() : item))
+    return el
+  }
+
+  /**
+   * Returns the XML serialization of this YXmlElement.
+   * The attributes are ordered by attribute-name, so you can easily use this
+   * method to compare YXmlElements
+   *
+   * @return {string} The string representation of this type.
+   *
+   * @public
+   */
+  toString () {
+    const attrs = this.getAttributes()
+    const stringBuilder = []
+    const keys = []
+    for (const key in attrs) {
+      keys.push(key)
+    }
+    keys.sort()
+    const keysLen = keys.length
+    for (let i = 0; i < keysLen; i++) {
+      const key = keys[i]
+      stringBuilder.push(key + '="' + attrs[key] + '"')
+    }
+    const nodeName = this.nodeName.toLocaleLowerCase()
+    const attrsString = stringBuilder.length > 0 ? ' ' + stringBuilder.join(' ') : ''
+    return `<${nodeName}${attrsString}>${super.toString()}</${nodeName}>`
+  }
+
+  /**
+   * Removes an attribute from this YXmlElement.
+   *
+   * @param {string} attributeName The attribute name that is to be removed.
+   *
+   * @public
+   */
+  removeAttribute (attributeName) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeMapDelete(transaction, this, attributeName)
+      })
+    } else {
+      /** @type {Map<string,any>} */ (this._prelimAttrs).delete(attributeName)
+    }
+  }
+
+  /**
+   * Sets or updates an attribute.
+   *
+   * @template {keyof KV & string} KEY
+   *
+   * @param {KEY} attributeName The attribute name that is to be set.
+   * @param {KV[KEY]} 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.
+   *
+   * @template {keyof KV & string} KEY
+   *
+   * @param {KEY} attributeName The attribute name that identifies the
+   *                               queried value.
+   * @return {KV[KEY]|undefined} The queried attribute value.
+   *
+   * @public
+   */
+  getAttribute (attributeName) {
+    return /** @type {any} */ (typeMapGet(this, attributeName))
+  }
+
+  /**
+   * Returns whether an attribute exists
+   *
+   * @param {string} attributeName The attribute name to check for existence.
+   * @return {boolean} whether the attribute exists.
+   *
+   * @public
+   */
+  hasAttribute (attributeName) {
+    return /** @type {any} */ (typeMapHas(this, attributeName))
+  }
+
+  /**
+   * Returns all attribute name/value pairs in a JSON Object.
+   *
+   * @param {Snapshot} [snapshot]
+   * @return {{ [Key in Extract<keyof KV,string>]?: KV[Key]}} A JSON Object that describes the attributes.
+   *
+   * @public
+   */
+  getAttributes (snapshot) {
+    return /** @type {any} */ (snapshot ? typeMapGetAllSnapshot(this, snapshot) : 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) {
+      const value = attrs[key]
+      if (typeof value === 'string') {
+        dom.setAttribute(key, value)
+      }
+    }
+    typeListForEach(this, yxml => {
+      dom.appendChild(yxml.toDOM(_document, hooks, binding))
+    })
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlElementRefID)
+    encoder.writeKey(this.nodeName)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlElement}
+ *
+ * @function
+ */
+export const readYXmlElement = decoder => new YXmlElement(decoder.readKey())
--- a/src/types/YXmlEvent.js
+++ b/src/types/YXmlEvent.js
@ -0,0 +1,39 @@
+import {
+  YEvent,
+  YXmlText, YXmlElement, YXmlFragment, Transaction // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * @extends YEvent<YXmlElement|YXmlText|YXmlFragment>
+ * An Event that describes changes on a YXml Element or Yxml Fragment
+ */
+export class YXmlEvent extends YEvent {
+  /**
+   * @param {YXmlElement|YXmlText|YXmlFragment} target The target on which the event is created.
+   * @param {Set<string|null>} subs The set of changed attributes. `null` is included if the
+   *                   child list changed.
+   * @param {Transaction} transaction The transaction instance with which the
+   *                                  change was created.
+   */
+  constructor (target, subs, transaction) {
+    super(target, transaction)
+    /**
+     * Whether the children changed.
+     * @type {Boolean}
+     * @private
+     */
+    this.childListChanged = false
+    /**
+     * Set of all changed attributes.
+     * @type {Set<string>}
+     */
+    this.attributesChanged = new Set()
+    subs.forEach((sub) => {
+      if (sub === null) {
+        this.childListChanged = true
+      } else {
+        this.attributesChanged.add(sub)
+      }
+    })
+  }
+}
--- a/src/types/YXmlFragment.js
+++ b/src/types/YXmlFragment.js
@ -0,0 +1,449 @@
+/**
+ * @module YXml
+ */
+
+import {
+  YXmlEvent,
+  YXmlElement,
+  AbstractType,
+  typeListMap,
+  typeListForEach,
+  typeListInsertGenerics,
+  typeListInsertGenericsAfter,
+  typeListDelete,
+  typeListToArray,
+  YXmlFragmentRefID,
+  callTypeObservers,
+  transact,
+  typeListGet,
+  typeListSlice,
+  warnPrematureAccess,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, Doc, ContentType, Transaction, Item, YXmlText, YXmlHook // eslint-disable-line
+} from '../internals.js'
+
+import * as error from 'lib0/error'
+import * as array from 'lib0/array'
+
+/**
+ * Define the elements to which a set of CSS queries apply.
+ * {@link https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Selectors|CSS_Selectors}
+ *
+ * @example
+ *   query = '.classSelector'
+ *   query = 'nodeSelector'
+ *   query = '#idSelector'
+ *
+ * @typedef {string} CSS_Selector
+ */
+
+/**
+ * Dom filter function.
+ *
+ * @callback domFilter
+ * @param {string} nodeName The nodeName of the element
+ * @param {Map} attributes The map of attributes.
+ * @return {boolean} Whether to include the Dom node in the YXmlElement.
+ */
+
+/**
+ * Represents a subset of the nodes of a YXmlElement / YXmlFragment and a
+ * position within them.
+ *
+ * Can be created with {@link YXmlFragment#createTreeWalker}
+ *
+ * @public
+ * @implements {Iterable<YXmlElement|YXmlText|YXmlElement|YXmlHook>}
+ */
+export class YXmlTreeWalker {
+  /**
+   * @param {YXmlFragment | YXmlElement} root
+   * @param {function(AbstractType<any>):boolean} [f]
+   */
+  constructor (root, f = () => true) {
+    this._filter = f
+    this._root = root
+    /**
+     * @type {Item}
+     */
+    this._currentNode = /** @type {Item} */ (root._start)
+    this._firstCall = true
+    root.doc ?? warnPrematureAccess()
+  }
+
+  [Symbol.iterator] () {
+    return this
+  }
+
+  /**
+   * Get the next node.
+   *
+   * @return {IteratorResult<YXmlElement|YXmlText|YXmlHook>} The next node.
+   *
+   * @public
+   */
+  next () {
+    /**
+     * @type {Item|null}
+     */
+    let n = this._currentNode
+    let type = n && n.content && /** @type {any} */ (n.content).type
+    if (n !== null && (!this._firstCall || n.deleted || !this._filter(type))) { // if first call, we check if we can use the first item
+      do {
+        type = /** @type {any} */ (n.content).type
+        if (!n.deleted && (type.constructor === YXmlElement || type.constructor === YXmlFragment) && type._start !== null) {
+          // walk down in the tree
+          n = type._start
+        } else {
+          // walk right or up in the tree
+          while (n !== null) {
+            /**
+             * @type {Item | null}
+             */
+            const nxt = n.next
+            if (nxt !== null) {
+              n = nxt
+              break
+            } else if (n.parent === this._root) {
+              n = null
+            } else {
+              n = /** @type {AbstractType<any>} */ (n.parent)._item
+            }
+          }
+        }
+      } while (n !== null && (n.deleted || !this._filter(/** @type {ContentType} */ (n.content).type)))
+    }
+    this._firstCall = false
+    if (n === null) {
+      // @ts-ignore
+      return { value: undefined, done: true }
+    }
+    this._currentNode = n
+    return { value: /** @type {any} */ (n.content).type, done: false }
+  }
+}
+
+/**
+ * Represents a list of {@link YXmlElement}.and {@link YXmlText} types.
+ * A YxmlFragment is similar to a {@link YXmlElement}, but it does not have a
+ * nodeName and it does not have attributes. Though it can be bound to a DOM
+ * element - in this case the attributes and the nodeName are not shared.
+ *
+ * @public
+ * @extends AbstractType<YXmlEvent>
+ */
+export class YXmlFragment extends AbstractType {
+  constructor () {
+    super()
+    /**
+     * @type {Array<any>|null}
+     */
+    this._prelimContent = []
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get firstChild () {
+    const first = this._first
+    return first ? first.content.getContent()[0] : null
+  }
+
+  /**
+   * Integrate this type into the Yjs instance.
+   *
+   * * Save this struct in the os
+   * * This type is sent to other client
+   * * Observer functions are fired
+   *
+   * @param {Doc} y The Yjs instance
+   * @param {Item} item
+   */
+  _integrate (y, item) {
+    super._integrate(y, item)
+    this.insert(0, /** @type {Array<any>} */ (this._prelimContent))
+    this._prelimContent = null
+  }
+
+  _copy () {
+    return new YXmlFragment()
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YXmlFragment}
+   */
+  clone () {
+    const el = new YXmlFragment()
+    // @ts-ignore
+    el.insert(0, this.toArray().map(item => item instanceof AbstractType ? item.clone() : item))
+    return el
+  }
+
+  get length () {
+    this.doc ?? warnPrematureAccess()
+    return this._prelimContent === null ? this._length : this._prelimContent.length
+  }
+
+  /**
+   * Create a subtree of childNodes.
+   *
+   * @example
+   * const walker = elem.createTreeWalker(dom => dom.nodeName === 'div')
+   * for (let node in walker) {
+   *   // `node` is a div node
+   *   nop(node)
+   * }
+   *
+   * @param {function(AbstractType<any>):boolean} filter Function that is called on each child element and
+   *                          returns a Boolean indicating whether the child
+   *                          is to be included in the subtree.
+   * @return {YXmlTreeWalker} A subtree and a position within it.
+   *
+   * @public
+   */
+  createTreeWalker (filter) {
+    return new YXmlTreeWalker(this, filter)
+  }
+
+  /**
+   * Returns the first YXmlElement that matches the query.
+   * Similar to DOM's {@link querySelector}.
+   *
+   * Query support:
+   *   - tagname
+   * TODO:
+   *   - id
+   *   - attribute
+   *
+   * @param {CSS_Selector} query The query on the children.
+   * @return {YXmlElement|YXmlText|YXmlHook|null} The first element that matches the query or null.
+   *
+   * @public
+   */
+  querySelector (query) {
+    query = query.toUpperCase()
+    // @ts-ignore
+    const iterator = new YXmlTreeWalker(this, element => element.nodeName && element.nodeName.toUpperCase() === query)
+    const next = iterator.next()
+    if (next.done) {
+      return null
+    } else {
+      return next.value
+    }
+  }
+
+  /**
+   * Returns all YXmlElements that match the query.
+   * Similar to Dom's {@link querySelectorAll}.
+   *
+   * @todo Does not yet support all queries. Currently only query by tagName.
+   *
+   * @param {CSS_Selector} query The query on the children
+   * @return {Array<YXmlElement|YXmlText|YXmlHook|null>} The elements that match this query.
+   *
+   * @public
+   */
+  querySelectorAll (query) {
+    query = query.toUpperCase()
+    // @ts-ignore
+    return array.from(new YXmlTreeWalker(this, element => element.nodeName && element.nodeName.toUpperCase() === query))
+  }
+
+  /**
+   * Creates YXmlEvent and calls observers.
+   *
+   * @param {Transaction} transaction
+   * @param {Set<null|string>} parentSubs Keys changed on this type. `null` if list was modified.
+   */
+  _callObserver (transaction, parentSubs) {
+    callTypeObservers(this, transaction, new YXmlEvent(this, parentSubs, transaction))
+  }
+
+  /**
+   * Get the string representation of all the children of this YXmlFragment.
+   *
+   * @return {string} The string representation of all children.
+   */
+  toString () {
+    return typeListMap(this, xml => xml.toString()).join('')
+  }
+
+  /**
+   * @return {string}
+   */
+  toJSON () {
+    return this.toString()
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlElement.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object<string, any>} [hooks={}] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type.
+   * @return {Node} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks = {}, binding) {
+    const fragment = _document.createDocumentFragment()
+    if (binding !== undefined) {
+      binding._createAssociation(fragment, this)
+    }
+    typeListForEach(this, xmlType => {
+      fragment.insertBefore(xmlType.toDOM(_document, hooks, binding), null)
+    })
+    return fragment
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  xml.insert(0, [new Y.XmlText('text')])
+   *
+   * @param {number} index The index to insert content at
+   * @param {Array<YXmlElement|YXmlText>} content The array of content
+   */
+  insert (index, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListInsertGenerics(transaction, this, index, content)
+      })
+    } else {
+      // @ts-ignore _prelimContent is defined because this is not yet integrated
+      this._prelimContent.splice(index, 0, ...content)
+    }
+  }
+
+  /**
+   * Inserts new content at an index.
+   *
+   * @example
+   *  // Insert character 'a' at position 0
+   *  xml.insert(0, [new Y.XmlText('text')])
+   *
+   * @param {null|Item|YXmlElement|YXmlText} ref The index to insert content at
+   * @param {Array<YXmlElement|YXmlText>} content The array of content
+   */
+  insertAfter (ref, content) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        const refItem = (ref && ref instanceof AbstractType) ? ref._item : ref
+        typeListInsertGenericsAfter(transaction, this, refItem, content)
+      })
+    } else {
+      const pc = /** @type {Array<any>} */ (this._prelimContent)
+      const index = ref === null ? 0 : pc.findIndex(el => el === ref) + 1
+      if (index === 0 && ref !== null) {
+        throw error.create('Reference item not found')
+      }
+      pc.splice(index, 0, ...content)
+    }
+  }
+
+  /**
+   * Deletes elements starting from an index.
+   *
+   * @param {number} index Index at which to start deleting elements
+   * @param {number} [length=1] The number of elements to remove. Defaults to 1.
+   */
+  delete (index, length = 1) {
+    if (this.doc !== null) {
+      transact(this.doc, transaction => {
+        typeListDelete(transaction, this, index, length)
+      })
+    } else {
+      // @ts-ignore _prelimContent is defined because this is not yet integrated
+      this._prelimContent.splice(index, length)
+    }
+  }
+
+  /**
+   * Transforms this YArray to a JavaScript Array.
+   *
+   * @return {Array<YXmlElement|YXmlText|YXmlHook>}
+   */
+  toArray () {
+    return typeListToArray(this)
+  }
+
+  /**
+   * Appends content to this YArray.
+   *
+   * @param {Array<YXmlElement|YXmlText>} content Array of content to append.
+   */
+  push (content) {
+    this.insert(this.length, content)
+  }
+
+  /**
+   * Prepends content to this YArray.
+   *
+   * @param {Array<YXmlElement|YXmlText>} content Array of content to prepend.
+   */
+  unshift (content) {
+    this.insert(0, content)
+  }
+
+  /**
+   * Returns the i-th element from a YArray.
+   *
+   * @param {number} index The index of the element to return from the YArray
+   * @return {YXmlElement|YXmlText}
+   */
+  get (index) {
+    return typeListGet(this, index)
+  }
+
+  /**
+   * Returns a portion of this YXmlFragment into a JavaScript Array selected
+   * from start to end (end not included).
+   *
+   * @param {number} [start]
+   * @param {number} [end]
+   * @return {Array<YXmlElement|YXmlText>}
+   */
+  slice (start = 0, end = this.length) {
+    return typeListSlice(this, start, end)
+  }
+
+  /**
+   * Executes a provided function on once on every child element.
+   *
+   * @param {function(YXmlElement|YXmlText,number, typeof self):void} f A function to execute on every element of this YArray.
+   */
+  forEach (f) {
+    typeListForEach(this, f)
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlFragmentRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} _decoder
+ * @return {YXmlFragment}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlFragment = _decoder => new YXmlFragment()
--- a/src/types/YXmlHook.js
+++ b/src/types/YXmlHook.js
@ -0,0 +1,98 @@
+import {
+  YMap,
+  YXmlHookRefID,
+  UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2 // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * You can manage binding to a custom type with YXmlHook.
+ *
+ * @extends {YMap<any>}
+ */
+export class YXmlHook extends YMap {
+  /**
+   * @param {string} hookName nodeName of the Dom Node.
+   */
+  constructor (hookName) {
+    super()
+    /**
+     * @type {string}
+     */
+    this.hookName = hookName
+  }
+
+  /**
+   * Creates an Item with the same effect as this Item (without position effect)
+   */
+  _copy () {
+    return new YXmlHook(this.hookName)
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YXmlHook}
+   */
+  clone () {
+    const el = new YXmlHook(this.hookName)
+    this.forEach((value, key) => {
+      el.set(key, value)
+    })
+    return el
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlElement.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object.<string, any>} [hooks] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type
+   * @return {Element} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks = {}, binding) {
+    const hook = hooks[this.hookName]
+    let dom
+    if (hook !== undefined) {
+      dom = hook.createDom(this)
+    } else {
+      dom = document.createElement(this.hookName)
+    }
+    dom.setAttribute('data-yjs-hook', this.hookName)
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  /**
+   * Transform the properties of this type to binary and write it to an
+   * BinaryEncoder.
+   *
+   * This is called when this Item is sent to a remote peer.
+   *
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder The encoder to write data to.
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlHookRefID)
+    encoder.writeKey(this.hookName)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlHook}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlHook = decoder =>
+  new YXmlHook(decoder.readKey())
--- a/src/types/YXmlText.js
+++ b/src/types/YXmlText.js
@ -0,0 +1,124 @@
+import {
+  YText,
+  YXmlTextRefID,
+  ContentType, YXmlElement, UpdateDecoderV1, UpdateDecoderV2, UpdateEncoderV1, UpdateEncoderV2, // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * Represents text in a Dom Element. In the future this type will also handle
+ * simple formatting information like bold and italic.
+ */
+export class YXmlText extends YText {
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get nextSibling () {
+    const n = this._item ? this._item.next : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  /**
+   * @type {YXmlElement|YXmlText|null}
+   */
+  get prevSibling () {
+    const n = this._item ? this._item.prev : null
+    return n ? /** @type {YXmlElement|YXmlText} */ (/** @type {ContentType} */ (n.content).type) : null
+  }
+
+  _copy () {
+    return new YXmlText()
+  }
+
+  /**
+   * Makes a copy of this data type that can be included somewhere else.
+   *
+   * Note that the content is only readable _after_ it has been included somewhere in the Ydoc.
+   *
+   * @return {YXmlText}
+   */
+  clone () {
+    const text = new YXmlText()
+    text.applyDelta(this.toDelta())
+    return text
+  }
+
+  /**
+   * Creates a Dom Element that mirrors this YXmlText.
+   *
+   * @param {Document} [_document=document] The document object (you must define
+   *                                        this when calling this method in
+   *                                        nodejs)
+   * @param {Object<string, any>} [hooks] Optional property to customize how hooks
+   *                                             are presented in the DOM
+   * @param {any} [binding] You should not set this property. This is
+   *                               used if DomBinding wants to create a
+   *                               association to the created DOM type.
+   * @return {Text} The {@link https://developer.mozilla.org/en-US/docs/Web/API/Element|Dom Element}
+   *
+   * @public
+   */
+  toDOM (_document = document, hooks, binding) {
+    const dom = _document.createTextNode(this.toString())
+    if (binding !== undefined) {
+      binding._createAssociation(dom, this)
+    }
+    return dom
+  }
+
+  toString () {
+    // @ts-ignore
+    return this.toDelta().map(delta => {
+      const nestedNodes = []
+      for (const nodeName in delta.attributes) {
+        const attrs = []
+        for (const key in delta.attributes[nodeName]) {
+          attrs.push({ key, value: delta.attributes[nodeName][key] })
+        }
+        // sort attributes to get a unique order
+        attrs.sort((a, b) => a.key < b.key ? -1 : 1)
+        nestedNodes.push({ nodeName, attrs })
+      }
+      // sort node order to get a unique order
+      nestedNodes.sort((a, b) => a.nodeName < b.nodeName ? -1 : 1)
+      // now convert to dom string
+      let str = ''
+      for (let i = 0; i < nestedNodes.length; i++) {
+        const node = nestedNodes[i]
+        str += `<${node.nodeName}`
+        for (let j = 0; j < node.attrs.length; j++) {
+          const attr = node.attrs[j]
+          str += ` ${attr.key}="${attr.value}"`
+        }
+        str += '>'
+      }
+      str += delta.insert
+      for (let i = nestedNodes.length - 1; i >= 0; i--) {
+        str += `</${nestedNodes[i].nodeName}>`
+      }
+      return str
+    }).join('')
+  }
+
+  /**
+   * @return {string}
+   */
+  toJSON () {
+    return this.toString()
+  }
+
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  _write (encoder) {
+    encoder.writeTypeRef(YXmlTextRefID)
+  }
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ * @return {YXmlText}
+ *
+ * @private
+ * @function
+ */
+export const readYXmlText = decoder => new YXmlText()
--- a/src/utils/AbstractConnector.js
+++ b/src/utils/AbstractConnector.js
@ -0,0 +1,25 @@
+import { ObservableV2 } from 'lib0/observable'
+
+import {
+  Doc // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * This is an abstract interface that all Connectors should implement to keep them interchangeable.
+ *
+ * @note This interface is experimental and it is not advised to actually inherit this class.
+ *       It just serves as typing information.
+ *
+ * @extends {ObservableV2<any>}
+ */
+export class AbstractConnector extends ObservableV2 {
+  /**
+   * @param {Doc} ydoc
+   * @param {any} awareness
+   */
+  constructor (ydoc, awareness) {
+    super()
+    this.doc = ydoc
+    this.awareness = awareness
+  }
+}
--- a/src/utils/DeleteSet.js
+++ b/src/utils/DeleteSet.js
@ -0,0 +1,349 @@
+import {
+  findIndexSS,
+  getState,
+  splitItem,
+  iterateStructs,
+  UpdateEncoderV2,
+  DSDecoderV1, DSEncoderV1, DSDecoderV2, DSEncoderV2, Item, GC, StructStore, Transaction, ID // eslint-disable-line
+} from '../internals.js'
+
+import * as array from 'lib0/array'
+import * as math from 'lib0/math'
+import * as map from 'lib0/map'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+
+export class DeleteItem {
+  /**
+   * @param {number} clock
+   * @param {number} len
+   */
+  constructor (clock, len) {
+    /**
+     * @type {number}
+     */
+    this.clock = clock
+    /**
+     * @type {number}
+     */
+    this.len = len
+  }
+}
+
+/**
+ * We no longer maintain a DeleteStore. DeleteSet is a temporary object that is created when needed.
+ * - When created in a transaction, it must only be accessed after sorting, and merging
+ *   - This DeleteSet is send to other clients
+ * - We do not create a DeleteSet when we send a sync message. The DeleteSet message is created directly from StructStore
+ * - We read a DeleteSet as part of a sync/update message. In this case the DeleteSet is already sorted and merged.
+ */
+export class DeleteSet {
+  constructor () {
+    /**
+     * @type {Map<number,Array<DeleteItem>>}
+     */
+    this.clients = new Map()
+  }
+}
+
+/**
+ * Iterate over all structs that the DeleteSet gc's.
+ *
+ * @param {Transaction} transaction
+ * @param {DeleteSet} ds
+ * @param {function(GC|Item):void} f
+ *
+ * @function
+ */
+export const iterateDeletedStructs = (transaction, ds, f) =>
+  ds.clients.forEach((deletes, clientid) => {
+    const structs = /** @type {Array<GC|Item>} */ (transaction.doc.store.clients.get(clientid))
+    for (let i = 0; i < deletes.length; i++) {
+      const del = deletes[i]
+      iterateStructs(transaction, structs, del.clock, del.len, f)
+    }
+  })
+
+/**
+ * @param {Array<DeleteItem>} dis
+ * @param {number} clock
+ * @return {number|null}
+ *
+ * @private
+ * @function
+ */
+export const findIndexDS = (dis, clock) => {
+  let left = 0
+  let right = dis.length - 1
+  while (left <= right) {
+    const midindex = math.floor((left + right) / 2)
+    const mid = dis[midindex]
+    const midclock = mid.clock
+    if (midclock <= clock) {
+      if (clock < midclock + mid.len) {
+        return midindex
+      }
+      left = midindex + 1
+    } else {
+      right = midindex - 1
+    }
+  }
+  return null
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {ID} id
+ * @return {boolean}
+ *
+ * @private
+ * @function
+ */
+export const isDeleted = (ds, id) => {
+  const dis = ds.clients.get(id.client)
+  return dis !== undefined && findIndexDS(dis, id.clock) !== null
+}
+
+/**
+ * @param {DeleteSet} ds
+ *
+ * @private
+ * @function
+ */
+export const sortAndMergeDeleteSet = ds => {
+  ds.clients.forEach(dels => {
+    dels.sort((a, b) => a.clock - b.clock)
+    // merge items without filtering or splicing the array
+    // i is the current pointer
+    // j refers to the current insert position for the pointed item
+    // try to merge dels[i] into dels[j-1] or set dels[j]=dels[i]
+    let i, j
+    for (i = 1, j = 1; i < dels.length; i++) {
+      const left = dels[j - 1]
+      const right = dels[i]
+      if (left.clock + left.len >= right.clock) {
+        left.len = math.max(left.len, right.clock + right.len - left.clock)
+      } else {
+        if (j < i) {
+          dels[j] = right
+        }
+        j++
+      }
+    }
+    dels.length = j
+  })
+}
+
+/**
+ * @param {Array<DeleteSet>} dss
+ * @return {DeleteSet} A fresh DeleteSet
+ */
+export const mergeDeleteSets = dss => {
+  const merged = new DeleteSet()
+  for (let dssI = 0; dssI < dss.length; dssI++) {
+    dss[dssI].clients.forEach((delsLeft, client) => {
+      if (!merged.clients.has(client)) {
+        // Write all missing keys from current ds and all following.
+        // If merged already contains `client` current ds has already been added.
+        /**
+         * @type {Array<DeleteItem>}
+         */
+        const dels = delsLeft.slice()
+        for (let i = dssI + 1; i < dss.length; i++) {
+          array.appendTo(dels, dss[i].clients.get(client) || [])
+        }
+        merged.clients.set(client, dels)
+      }
+    })
+  }
+  sortAndMergeDeleteSet(merged)
+  return merged
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {number} client
+ * @param {number} clock
+ * @param {number} length
+ *
+ * @private
+ * @function
+ */
+export const addToDeleteSet = (ds, client, clock, length) => {
+  map.setIfUndefined(ds.clients, client, () => /** @type {Array<DeleteItem>} */ ([])).push(new DeleteItem(clock, length))
+}
+
+export const createDeleteSet = () => new DeleteSet()
+
+/**
+ * @param {StructStore} ss
+ * @return {DeleteSet} Merged and sorted DeleteSet
+ *
+ * @private
+ * @function
+ */
+export const createDeleteSetFromStructStore = ss => {
+  const ds = createDeleteSet()
+  ss.clients.forEach((structs, client) => {
+    /**
+     * @type {Array<DeleteItem>}
+     */
+    const dsitems = []
+    for (let i = 0; i < structs.length; i++) {
+      const struct = structs[i]
+      if (struct.deleted) {
+        const clock = struct.id.clock
+        let len = struct.length
+        if (i + 1 < structs.length) {
+          for (let next = structs[i + 1]; i + 1 < structs.length && next.deleted; next = structs[++i + 1]) {
+            len += next.length
+          }
+        }
+        dsitems.push(new DeleteItem(clock, len))
+      }
+    }
+    if (dsitems.length > 0) {
+      ds.clients.set(client, dsitems)
+    }
+  })
+  return ds
+}
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {DeleteSet} ds
+ *
+ * @private
+ * @function
+ */
+export const writeDeleteSet = (encoder, ds) => {
+  encoding.writeVarUint(encoder.restEncoder, ds.clients.size)
+
+  // Ensure that the delete set is written in a deterministic order
+  array.from(ds.clients.entries())
+    .sort((a, b) => b[0] - a[0])
+    .forEach(([client, dsitems]) => {
+      encoder.resetDsCurVal()
+      encoding.writeVarUint(encoder.restEncoder, client)
+      const len = dsitems.length
+      encoding.writeVarUint(encoder.restEncoder, len)
+      for (let i = 0; i < len; i++) {
+        const item = dsitems[i]
+        encoder.writeDsClock(item.clock)
+        encoder.writeDsLen(item.len)
+      }
+    })
+}
+
+/**
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @return {DeleteSet}
+ *
+ * @private
+ * @function
+ */
+export const readDeleteSet = decoder => {
+  const ds = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numClients; i++) {
+    decoder.resetDsCurVal()
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const numberOfDeletes = decoding.readVarUint(decoder.restDecoder)
+    if (numberOfDeletes > 0) {
+      const dsField = map.setIfUndefined(ds.clients, client, () => /** @type {Array<DeleteItem>} */ ([]))
+      for (let i = 0; i < numberOfDeletes; i++) {
+        dsField.push(new DeleteItem(decoder.readDsClock(), decoder.readDsLen()))
+      }
+    }
+  }
+  return ds
+}
+
+/**
+ * @todo YDecoder also contains references to String and other Decoders. Would make sense to exchange YDecoder.toUint8Array for YDecoder.DsToUint8Array()..
+ */
+
+/**
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @return {Uint8Array|null} Returns a v2 update containing all deletes that couldn't be applied yet; or null if all deletes were applied successfully.
+ *
+ * @private
+ * @function
+ */
+export const readAndApplyDeleteSet = (decoder, transaction, store) => {
+  const unappliedDS = new DeleteSet()
+  const numClients = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numClients; i++) {
+    decoder.resetDsCurVal()
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const numberOfDeletes = decoding.readVarUint(decoder.restDecoder)
+    const structs = store.clients.get(client) || []
+    const state = getState(store, client)
+    for (let i = 0; i < numberOfDeletes; i++) {
+      const clock = decoder.readDsClock()
+      const clockEnd = clock + decoder.readDsLen()
+      if (clock < state) {
+        if (state < clockEnd) {
+          addToDeleteSet(unappliedDS, client, state, clockEnd - state)
+        }
+        let index = findIndexSS(structs, clock)
+        /**
+         * We can ignore the case of GC and Delete structs, because we are going to skip them
+         * @type {Item}
+         */
+        // @ts-ignore
+        let struct = structs[index]
+        // split the first item if necessary
+        if (!struct.deleted && struct.id.clock < clock) {
+          structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock))
+          index++ // increase we now want to use the next struct
+        }
+        while (index < structs.length) {
+          // @ts-ignore
+          struct = structs[index++]
+          if (struct.id.clock < clockEnd) {
+            if (!struct.deleted) {
+              if (clockEnd < struct.id.clock + struct.length) {
+                structs.splice(index, 0, splitItem(transaction, struct, clockEnd - struct.id.clock))
+              }
+              struct.delete(transaction)
+            }
+          } else {
+            break
+          }
+        }
+      } else {
+        addToDeleteSet(unappliedDS, client, clock, clockEnd - clock)
+      }
+    }
+  }
+  if (unappliedDS.clients.size > 0) {
+    const ds = new UpdateEncoderV2()
+    encoding.writeVarUint(ds.restEncoder, 0) // encode 0 structs
+    writeDeleteSet(ds, unappliedDS)
+    return ds.toUint8Array()
+  }
+  return null
+}
+
+/**
+ * @param {DeleteSet} ds1
+ * @param {DeleteSet} ds2
+ */
+export const equalDeleteSets = (ds1, ds2) => {
+  if (ds1.clients.size !== ds2.clients.size) return false
+  for (const [client, deleteItems1] of ds1.clients.entries()) {
+    const deleteItems2 = /** @type {Array<import('../internals.js').DeleteItem>} */ (ds2.clients.get(client))
+    if (deleteItems2 === undefined || deleteItems1.length !== deleteItems2.length) return false
+    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) {
+        return false
+      }
+    }
+  }
+  return true
+}
--- a/src/utils/Doc.js
+++ b/src/utils/Doc.js
@ -0,0 +1,347 @@
+/**
+ * @module Y
+ */
+
+import {
+  StructStore,
+  AbstractType,
+  YArray,
+  YText,
+  YMap,
+  YXmlElement,
+  YXmlFragment,
+  transact,
+  ContentDoc, Item, Transaction, YEvent // eslint-disable-line
+} from '../internals.js'
+
+import { ObservableV2 } from 'lib0/observable'
+import * as random from 'lib0/random'
+import * as map from 'lib0/map'
+import * as array from 'lib0/array'
+import * as promise from 'lib0/promise'
+
+export const generateNewClientId = random.uint32
+
+/**
+ * @typedef {Object} DocOpts
+ * @property {boolean} [DocOpts.gc=true] Disable garbage collection (default: gc=true)
+ * @property {function(Item):boolean} [DocOpts.gcFilter] Will be called before an Item is garbage collected. Return false to keep the Item.
+ * @property {string} [DocOpts.guid] Define a globally unique identifier for this document
+ * @property {string | null} [DocOpts.collectionid] Associate this document with a collection. This only plays a role if your provider has a concept of collection.
+ * @property {any} [DocOpts.meta] Any kind of meta information you want to associate with this document. If this is a subdocument, remote peers will store the meta information as well.
+ * @property {boolean} [DocOpts.autoLoad] If a subdocument, automatically load document. If this is a subdocument, remote peers will load the document as well automatically.
+ * @property {boolean} [DocOpts.shouldLoad] Whether the document should be synced by the provider now. This is toggled to true when you call ydoc.load()
+ */
+
+/**
+ * @typedef {Object} DocEvents
+ * @property {function(Doc):void} DocEvents.destroy
+ * @property {function(Doc):void} DocEvents.load
+ * @property {function(boolean, Doc):void} DocEvents.sync
+ * @property {function(Uint8Array, any, Doc, Transaction):void} DocEvents.update
+ * @property {function(Uint8Array, any, Doc, Transaction):void} DocEvents.updateV2
+ * @property {function(Doc):void} DocEvents.beforeAllTransactions
+ * @property {function(Transaction, Doc):void} DocEvents.beforeTransaction
+ * @property {function(Transaction, Doc):void} DocEvents.beforeObserverCalls
+ * @property {function(Transaction, Doc):void} DocEvents.afterTransaction
+ * @property {function(Transaction, Doc):void} DocEvents.afterTransactionCleanup
+ * @property {function(Doc, Array<Transaction>):void} DocEvents.afterAllTransactions
+ * @property {function({ loaded: Set<Doc>, added: Set<Doc>, removed: Set<Doc> }, Doc, Transaction):void} DocEvents.subdocs
+ */
+
+/**
+ * A Yjs instance handles the state of shared data.
+ * @extends ObservableV2<DocEvents>
+ */
+export class Doc extends ObservableV2 {
+  /**
+   * @param {DocOpts} opts configuration
+   */
+  constructor ({ guid = random.uuidv4(), collectionid = null, gc = true, gcFilter = () => true, meta = null, autoLoad = false, shouldLoad = true } = {}) {
+    super()
+    this.gc = gc
+    this.gcFilter = gcFilter
+    this.clientID = generateNewClientId()
+    this.guid = guid
+    this.collectionid = collectionid
+    /**
+     * @type {Map<string, AbstractType<YEvent<any>>>}
+     */
+    this.share = new Map()
+    this.store = new StructStore()
+    /**
+     * @type {Transaction | null}
+     */
+    this._transaction = null
+    /**
+     * @type {Array<Transaction>}
+     */
+    this._transactionCleanups = []
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocs = new Set()
+    /**
+     * If this document is a subdocument - a document integrated into another document - then _item is defined.
+     * @type {Item?}
+     */
+    this._item = null
+    this.shouldLoad = shouldLoad
+    this.autoLoad = autoLoad
+    this.meta = meta
+    /**
+     * This is set to true when the persistence provider loaded the document from the database or when the `sync` event fires.
+     * Note that not all providers implement this feature. Provider authors are encouraged to fire the `load` event when the doc content is loaded from the database.
+     *
+     * @type {boolean}
+     */
+    this.isLoaded = false
+    /**
+     * This is set to true when the connection provider has successfully synced with a backend.
+     * Note that when using peer-to-peer providers this event may not provide very useful.
+     * Also note that not all providers implement this feature. Provider authors are encouraged to fire
+     * the `sync` event when the doc has been synced (with `true` as a parameter) or if connection is
+     * lost (with false as a parameter).
+     */
+    this.isSynced = false
+    this.isDestroyed = false
+    /**
+     * Promise that resolves once the document has been loaded from a persistence provider.
+     */
+    this.whenLoaded = promise.create(resolve => {
+      this.on('load', () => {
+        this.isLoaded = true
+        resolve(this)
+      })
+    })
+    const provideSyncedPromise = () => promise.create(resolve => {
+      /**
+       * @param {boolean} isSynced
+       */
+      const eventHandler = (isSynced) => {
+        if (isSynced === undefined || isSynced === true) {
+          this.off('sync', eventHandler)
+          resolve()
+        }
+      }
+      this.on('sync', eventHandler)
+    })
+    this.on('sync', isSynced => {
+      if (isSynced === false && this.isSynced) {
+        this.whenSynced = provideSyncedPromise()
+      }
+      this.isSynced = isSynced === undefined || isSynced === true
+      if (this.isSynced && !this.isLoaded) {
+        this.emit('load', [this])
+      }
+    })
+    /**
+     * Promise that resolves once the document has been synced with a backend.
+     * This promise is recreated when the connection is lost.
+     * Note the documentation about the `isSynced` property.
+     */
+    this.whenSynced = provideSyncedPromise()
+  }
+
+  /**
+   * Notify the parent document that you request to load data into this subdocument (if it is a subdocument).
+   *
+   * `load()` might be used in the future to request any provider to load the most current data.
+   *
+   * It is safe to call `load()` multiple times.
+   */
+  load () {
+    const item = this._item
+    if (item !== null && !this.shouldLoad) {
+      transact(/** @type {any} */ (item.parent).doc, transaction => {
+        transaction.subdocsLoaded.add(this)
+      }, null, true)
+    }
+    this.shouldLoad = true
+  }
+
+  getSubdocs () {
+    return this.subdocs
+  }
+
+  getSubdocGuids () {
+    return new Set(array.from(this.subdocs).map(doc => doc.guid))
+  }
+
+  /**
+   * Changes that happen inside of a transaction are bundled. This means that
+   * the observer fires _after_ the transaction is finished and that all changes
+   * that happened inside of the transaction are sent as one message to the
+   * other peers.
+   *
+   * @template T
+   * @param {function(Transaction):T} 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
+   * @return T
+   *
+   * @public
+   */
+  transact (f, origin = null) {
+    return transact(this, f, origin)
+  }
+
+  /**
+   * Define a shared data type.
+   *
+   * Multiple calls of `ydoc.get(name, TypeConstructor)` yield the same result
+   * and do not overwrite each other. I.e.
+   * `ydoc.get(name, Y.Array) === ydoc.get(name, Y.Array)`
+   *
+   * After this method is called, the type is also available on `ydoc.share.get(name)`.
+   *
+   * *Best Practices:*
+   * Define all types right after the Y.Doc instance is created and store them in a separate object.
+   * Also use the typed methods `getText(name)`, `getArray(name)`, ..
+   *
+   * @template {typeof AbstractType<any>} Type
+   * @example
+   *   const ydoc = new Y.Doc(..)
+   *   const appState = {
+   *     document: ydoc.getText('document')
+   *     comments: ydoc.getArray('comments')
+   *   }
+   *
+   * @param {string} name
+   * @param {Type} TypeConstructor The constructor of the type definition. E.g. Y.Text, Y.Array, Y.Map, ...
+   * @return {InstanceType<Type>} The created type. Constructed with TypeConstructor
+   *
+   * @public
+   */
+  get (name, TypeConstructor = /** @type {any} */ (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 /** @type {InstanceType<Type>} */ (t)
+      } else {
+        throw new Error(`Type with the name ${name} has already been defined with a different constructor`)
+      }
+    }
+    return /** @type {InstanceType<Type>} */ (type)
+  }
+
+  /**
+   * @template T
+   * @param {string} [name]
+   * @return {YArray<T>}
+   *
+   * @public
+   */
+  getArray (name = '') {
+    return /** @type {YArray<T>} */ (this.get(name, YArray))
+  }
+
+  /**
+   * @param {string} [name]
+   * @return {YText}
+   *
+   * @public
+   */
+  getText (name = '') {
+    return this.get(name, YText)
+  }
+
+  /**
+   * @template T
+   * @param {string} [name]
+   * @return {YMap<T>}
+   *
+   * @public
+   */
+  getMap (name = '') {
+    return /** @type {YMap<T>} */ (this.get(name, YMap))
+  }
+
+  /**
+   * @param {string} [name]
+   * @return {YXmlElement}
+   *
+   * @public
+   */
+  getXmlElement (name = '') {
+    return /** @type {YXmlElement<{[key:string]:string}>} */ (this.get(name, YXmlElement))
+  }
+
+  /**
+   * @param {string} [name]
+   * @return {YXmlFragment}
+   *
+   * @public
+   */
+  getXmlFragment (name = '') {
+    return this.get(name, YXmlFragment)
+  }
+
+  /**
+   * Converts the entire document into a js object, recursively traversing each yjs type
+   * Doesn't log types that have not been defined (using ydoc.getType(..)).
+   *
+   * @deprecated Do not use this method and rather call toJSON directly on the shared types.
+   *
+   * @return {Object<string, any>}
+   */
+  toJSON () {
+    /**
+     * @type {Object<string, any>}
+     */
+    const doc = {}
+
+    this.share.forEach((value, key) => {
+      doc[key] = value.toJSON()
+    })
+
+    return doc
+  }
+
+  /**
+   * Emit `destroy` event and unregister all event handlers.
+   */
+  destroy () {
+    this.isDestroyed = true
+    array.from(this.subdocs).forEach(subdoc => subdoc.destroy())
+    const item = this._item
+    if (item !== null) {
+      this._item = null
+      const content = /** @type {ContentDoc} */ (item.content)
+      content.doc = new Doc({ guid: this.guid, ...content.opts, shouldLoad: false })
+      content.doc._item = item
+      transact(/** @type {any} */ (item).parent.doc, transaction => {
+        const doc = content.doc
+        if (!item.deleted) {
+          transaction.subdocsAdded.add(doc)
+        }
+        transaction.subdocsRemoved.add(this)
+      }, null, true)
+    }
+    // @ts-ignore
+    this.emit('destroyed', [true]) // DEPRECATED!
+    this.emit('destroy', [this])
+    super.destroy()
+  }
+}
--- a/src/utils/EventHandler.js
+++ b/src/utils/EventHandler.js
@ -0,0 +1,87 @@
+import * as f from 'lib0/function'
+
+/**
+ * General event handler implementation.
+ *
+ * @template ARG0, ARG1
+ *
+ * @private
+ */
+export class EventHandler {
+  constructor () {
+    /**
+     * @type {Array<function(ARG0, ARG1):void>}
+     */
+    this.l = []
+  }
+}
+
+/**
+ * @template ARG0,ARG1
+ * @returns {EventHandler<ARG0,ARG1>}
+ *
+ * @private
+ * @function
+ */
+export const createEventHandler = () => new EventHandler()
+
+/**
+ * Adds an event listener that is called when
+ * {@link EventHandler#callEventListeners} is called.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {function(ARG0,ARG1):void} f The event handler.
+ *
+ * @private
+ * @function
+ */
+export const addEventHandlerListener = (eventHandler, f) =>
+  eventHandler.l.push(f)
+
+/**
+ * Removes an event listener.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {function(ARG0,ARG1):void} f The event handler that was added with
+ *                     {@link EventHandler#addEventListener}
+ *
+ * @private
+ * @function
+ */
+export const removeEventHandlerListener = (eventHandler, f) => {
+  const l = eventHandler.l
+  const len = l.length
+  eventHandler.l = l.filter(g => f !== g)
+  if (len === eventHandler.l.length) {
+    console.error('[yjs] Tried to remove event handler that doesn\'t exist.')
+  }
+}
+
+/**
+ * Removes all event listeners.
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ *
+ * @private
+ * @function
+ */
+export const removeAllEventHandlerListeners = eventHandler => {
+  eventHandler.l.length = 0
+}
+
+/**
+ * Call all event listeners that were added via
+ * {@link EventHandler#addEventListener}.
+ *
+ * @template ARG0,ARG1
+ * @param {EventHandler<ARG0,ARG1>} eventHandler
+ * @param {ARG0} arg0
+ * @param {ARG1} arg1
+ *
+ * @private
+ * @function
+ */
+export const callEventHandlerListeners = (eventHandler, arg0, arg1) =>
+  f.callAll(eventHandler.l, [arg0, arg1])
--- a/src/utils/ID.js
+++ b/src/utils/ID.js
@ -0,0 +1,89 @@
+import { AbstractType } from '../internals.js' // eslint-disable-line
+
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+import * as error from 'lib0/error'
+
+export class ID {
+  /**
+   * @param {number} client client id
+   * @param {number} clock unique per client id, continuous number
+   */
+  constructor (client, clock) {
+    /**
+     * Client id
+     * @type {number}
+     */
+    this.client = client
+    /**
+     * unique per client id, continuous number
+     * @type {number}
+     */
+    this.clock = clock
+  }
+}
+
+/**
+ * @param {ID | null} a
+ * @param {ID | null} b
+ * @return {boolean}
+ *
+ * @function
+ */
+export const compareIDs = (a, b) => a === b || (a !== null && b !== null && a.client === b.client && a.clock === b.clock)
+
+/**
+ * @param {number} client
+ * @param {number} clock
+ *
+ * @private
+ * @function
+ */
+export const createID = (client, clock) => new ID(client, clock)
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {ID} id
+ *
+ * @private
+ * @function
+ */
+export const writeID = (encoder, id) => {
+  encoding.writeVarUint(encoder, id.client)
+  encoding.writeVarUint(encoder, id.clock)
+}
+
+/**
+ * Read ID.
+ * * If first varUint read is 0xFFFFFF a RootID is returned.
+ * * Otherwise an ID is returned
+ *
+ * @param {decoding.Decoder} decoder
+ * @return {ID}
+ *
+ * @private
+ * @function
+ */
+export const readID = decoder =>
+  createID(decoding.readVarUint(decoder), decoding.readVarUint(decoder))
+
+/**
+ * The top types are mapped from y.share.get(keyname) => type.
+ * `type` does not store any information about the `keyname`.
+ * This function finds the correct `keyname` for `type` and throws otherwise.
+ *
+ * @param {AbstractType<any>} type
+ * @return {string}
+ *
+ * @private
+ * @function
+ */
+export const findRootTypeKey = type => {
+  // @ts-ignore _y must be defined, otherwise unexpected case
+  for (const [key, value] of type.doc.share.entries()) {
+    if (value === type) {
+      return key
+    }
+  }
+  throw error.unexpectedCase()
+}
--- a/src/utils/PermanentUserData.js
+++ b/src/utils/PermanentUserData.js
@ -0,0 +1,141 @@
+import {
+  YArray,
+  YMap,
+  readDeleteSet,
+  writeDeleteSet,
+  createDeleteSet,
+  DSEncoderV1, DSDecoderV1, ID, DeleteSet, YArrayEvent, Transaction, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as decoding from 'lib0/decoding'
+
+import { mergeDeleteSets, isDeleted } from './DeleteSet.js'
+
+export class PermanentUserData {
+  /**
+   * @param {Doc} doc
+   * @param {YMap<any>} [storeType]
+   */
+  constructor (doc, storeType = doc.getMap('users')) {
+    /**
+     * @type {Map<string,DeleteSet>}
+     */
+    const dss = new Map()
+    this.yusers = storeType
+    this.doc = doc
+    /**
+     * Maps from clientid to userDescription
+     *
+     * @type {Map<number,string>}
+     */
+    this.clients = new Map()
+    this.dss = dss
+    /**
+     * @param {YMap<any>} user
+     * @param {string} userDescription
+     */
+    const initUser = (user, userDescription) => {
+      /**
+       * @type {YArray<Uint8Array>}
+       */
+      const ds = user.get('ds')
+      const ids = user.get('ids')
+      const addClientId = /** @param {number} clientid */ clientid => this.clients.set(clientid, userDescription)
+      ds.observe(/** @param {YArrayEvent<any>} event */ event => {
+        event.changes.added.forEach(item => {
+          item.content.getContent().forEach(encodedDs => {
+            if (encodedDs instanceof Uint8Array) {
+              this.dss.set(userDescription, mergeDeleteSets([this.dss.get(userDescription) || createDeleteSet(), readDeleteSet(new DSDecoderV1(decoding.createDecoder(encodedDs)))]))
+            }
+          })
+        })
+      })
+      this.dss.set(userDescription, mergeDeleteSets(ds.map(encodedDs => readDeleteSet(new DSDecoderV1(decoding.createDecoder(encodedDs))))))
+      ids.observe(/** @param {YArrayEvent<any>} event */ event =>
+        event.changes.added.forEach(item => item.content.getContent().forEach(addClientId))
+      )
+      ids.forEach(addClientId)
+    }
+    // observe users
+    storeType.observe(event => {
+      event.keysChanged.forEach(userDescription =>
+        initUser(storeType.get(userDescription), userDescription)
+      )
+    })
+    // add initial data
+    storeType.forEach(initUser)
+  }
+
+  /**
+   * @param {Doc} doc
+   * @param {number} clientid
+   * @param {string} userDescription
+   * @param {Object} conf
+   * @param {function(Transaction, DeleteSet):boolean} [conf.filter]
+   */
+  setUserMapping (doc, clientid, userDescription, { filter = () => true } = {}) {
+    const users = this.yusers
+    let user = users.get(userDescription)
+    if (!user) {
+      user = new YMap()
+      user.set('ids', new YArray())
+      user.set('ds', new YArray())
+      users.set(userDescription, user)
+    }
+    user.get('ids').push([clientid])
+    users.observe(_event => {
+      setTimeout(() => {
+        const userOverwrite = users.get(userDescription)
+        if (userOverwrite !== user) {
+          // user was overwritten, port all data over to the next user object
+          // @todo Experiment with Y.Sets here
+          user = userOverwrite
+          // @todo iterate over old type
+          this.clients.forEach((_userDescription, clientid) => {
+            if (userDescription === _userDescription) {
+              user.get('ids').push([clientid])
+            }
+          })
+          const encoder = new DSEncoderV1()
+          const ds = this.dss.get(userDescription)
+          if (ds) {
+            writeDeleteSet(encoder, ds)
+            user.get('ds').push([encoder.toUint8Array()])
+          }
+        }
+      }, 0)
+    })
+    doc.on('afterTransaction', /** @param {Transaction} transaction */ transaction => {
+      setTimeout(() => {
+        const yds = user.get('ds')
+        const ds = transaction.deleteSet
+        if (transaction.local && ds.clients.size > 0 && filter(transaction, ds)) {
+          const encoder = new DSEncoderV1()
+          writeDeleteSet(encoder, ds)
+          yds.push([encoder.toUint8Array()])
+        }
+      })
+    })
+  }
+
+  /**
+   * @param {number} clientid
+   * @return {any}
+   */
+  getUserByClientId (clientid) {
+    return this.clients.get(clientid) || null
+  }
+
+  /**
+   * @param {ID} id
+   * @return {string | null}
+   */
+  getUserByDeletedId (id) {
+    for (const [userDescription, ds] of this.dss.entries()) {
+      if (isDeleted(ds, id)) {
+        return userDescription
+      }
+    }
+    return null
+  }
+}
--- a/src/utils/RelativePosition.js
+++ b/src/utils/RelativePosition.js
@ -0,0 +1,353 @@
+import {
+  writeID,
+  readID,
+  compareIDs,
+  getState,
+  findRootTypeKey,
+  Item,
+  createID,
+  ContentType,
+  followRedone,
+  getItem,
+  StructStore, ID, Doc, AbstractType, // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as error from 'lib0/error'
+
+/**
+ * A relative position is based on the Yjs model and is not affected by document changes.
+ * E.g. If you place a relative position before a certain character, it will always point to this character.
+ * If you place a relative position at the end of a type, it will always point to the end of the type.
+ *
+ * A numeric position is often unsuited for user selections, because it does not change when content is inserted
+ * before or after.
+ *
+ * ```Insert(0, 'x')('a|bc') = 'xa|bc'``` Where | is the relative position.
+ *
+ * One of the properties must be defined.
+ *
+ * @example
+ *   // Current cursor position is at position 10
+ *   const relativePosition = createRelativePositionFromIndex(yText, 10)
+ *   // modify yText
+ *   yText.insert(0, 'abc')
+ *   yText.delete(3, 10)
+ *   // Compute the cursor position
+ *   const absolutePosition = createAbsolutePositionFromRelativePosition(y, relativePosition)
+ *   absolutePosition.type === yText // => true
+ *   console.log('cursor location is ' + absolutePosition.index) // => cursor location is 3
+ *
+ */
+export class RelativePosition {
+  /**
+   * @param {ID|null} type
+   * @param {string|null} tname
+   * @param {ID|null} item
+   * @param {number} assoc
+   */
+  constructor (type, tname, item, assoc = 0) {
+    /**
+     * @type {ID|null}
+     */
+    this.type = type
+    /**
+     * @type {string|null}
+     */
+    this.tname = tname
+    /**
+     * @type {ID | null}
+     */
+    this.item = item
+    /**
+     * A relative position is associated to a specific character. By default
+     * assoc >= 0, the relative position is associated to the character
+     * after the meant position.
+     * I.e. position 1 in 'ab' is associated to character 'b'.
+     *
+     * If assoc < 0, then the relative position is associated to the character
+     * before the meant position.
+     *
+     * @type {number}
+     */
+    this.assoc = assoc
+  }
+}
+
+/**
+ * @param {RelativePosition} rpos
+ * @return {any}
+ */
+export const relativePositionToJSON = rpos => {
+  const json = {}
+  if (rpos.type) {
+    json.type = rpos.type
+  }
+  if (rpos.tname) {
+    json.tname = rpos.tname
+  }
+  if (rpos.item) {
+    json.item = rpos.item
+  }
+  if (rpos.assoc != null) {
+    json.assoc = rpos.assoc
+  }
+  return json
+}
+
+/**
+ * @param {any} json
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const createRelativePositionFromJSON = json => new RelativePosition(json.type == null ? null : createID(json.type.client, json.type.clock), json.tname ?? null, json.item == null ? null : createID(json.item.client, json.item.clock), json.assoc == null ? 0 : json.assoc)
+
+export class AbsolutePosition {
+  /**
+   * @param {AbstractType<any>} type
+   * @param {number} index
+   * @param {number} [assoc]
+   */
+  constructor (type, index, assoc = 0) {
+    /**
+     * @type {AbstractType<any>}
+     */
+    this.type = type
+    /**
+     * @type {number}
+     */
+    this.index = index
+    this.assoc = assoc
+  }
+}
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {number} index
+ * @param {number} [assoc]
+ *
+ * @function
+ */
+export const createAbsolutePosition = (type, index, assoc = 0) => new AbsolutePosition(type, index, assoc)
+
+/**
+ * @param {AbstractType<any>} type
+ * @param {ID|null} item
+ * @param {number} [assoc]
+ *
+ * @function
+ */
+export const createRelativePosition = (type, item, assoc) => {
+  let typeid = null
+  let tname = null
+  if (type._item === null) {
+    tname = findRootTypeKey(type)
+  } else {
+    typeid = createID(type._item.id.client, type._item.id.clock)
+  }
+  return new RelativePosition(typeid, tname, item, assoc)
+}
+
+/**
+ * Create a relativePosition based on a absolute position.
+ *
+ * @param {AbstractType<any>} type The base type (e.g. YText or YArray).
+ * @param {number} index The absolute position.
+ * @param {number} [assoc]
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const createRelativePositionFromTypeIndex = (type, index, assoc = 0) => {
+  let t = type._start
+  if (assoc < 0) {
+    // associated to the left character or the beginning of a type, increment index if possible.
+    if (index === 0) {
+      return createRelativePosition(type, null, assoc)
+    }
+    index--
+  }
+  while (t !== null) {
+    if (!t.deleted && t.countable) {
+      if (t.length > index) {
+        // case 1: found position somewhere in the linked list
+        return createRelativePosition(type, createID(t.id.client, t.id.clock + index), assoc)
+      }
+      index -= t.length
+    }
+    if (t.right === null && assoc < 0) {
+      // left-associated position, return last available id
+      return createRelativePosition(type, t.lastId, assoc)
+    }
+    t = t.right
+  }
+  return createRelativePosition(type, null, assoc)
+}
+
+/**
+ * @param {encoding.Encoder} encoder
+ * @param {RelativePosition} rpos
+ *
+ * @function
+ */
+export const writeRelativePosition = (encoder, rpos) => {
+  const { type, tname, item, assoc } = rpos
+  if (item !== null) {
+    encoding.writeVarUint(encoder, 0)
+    writeID(encoder, item)
+  } else if (tname !== null) {
+    // case 2: found position at the end of the list and type is stored in y.share
+    encoding.writeUint8(encoder, 1)
+    encoding.writeVarString(encoder, tname)
+  } else if (type !== null) {
+    // case 3: found position at the end of the list and type is attached to an item
+    encoding.writeUint8(encoder, 2)
+    writeID(encoder, type)
+  } else {
+    throw error.unexpectedCase()
+  }
+  encoding.writeVarInt(encoder, assoc)
+  return encoder
+}
+
+/**
+ * @param {RelativePosition} rpos
+ * @return {Uint8Array}
+ */
+export const encodeRelativePosition = rpos => {
+  const encoder = encoding.createEncoder()
+  writeRelativePosition(encoder, rpos)
+  return encoding.toUint8Array(encoder)
+}
+
+/**
+ * @param {decoding.Decoder} decoder
+ * @return {RelativePosition}
+ *
+ * @function
+ */
+export const readRelativePosition = decoder => {
+  let type = null
+  let tname = null
+  let itemID = null
+  switch (decoding.readVarUint(decoder)) {
+    case 0:
+      // case 1: found position somewhere in the linked list
+      itemID = readID(decoder)
+      break
+    case 1:
+      // case 2: found position at the end of the list and type is stored in y.share
+      tname = decoding.readVarString(decoder)
+      break
+    case 2: {
+      // case 3: found position at the end of the list and type is attached to an item
+      type = readID(decoder)
+    }
+  }
+  const assoc = decoding.hasContent(decoder) ? decoding.readVarInt(decoder) : 0
+  return new RelativePosition(type, tname, itemID, assoc)
+}
+
+/**
+ * @param {Uint8Array} uint8Array
+ * @return {RelativePosition}
+ */
+export const decodeRelativePosition = uint8Array => readRelativePosition(decoding.createDecoder(uint8Array))
+
+/**
+ * @param {StructStore} store
+ * @param {ID} id
+ */
+const getItemWithOffset = (store, id) => {
+  const item = getItem(store, id)
+  const diff = id.clock - item.id.clock
+  return {
+    item, diff
+  }
+}
+
+/**
+ * Transform a relative position to an absolute position.
+ *
+ * If you want to share the relative position with other users, you should set
+ * `followUndoneDeletions` to false to get consistent results across all clients.
+ *
+ * When calculating the absolute position, we try to follow the "undone deletions". This yields
+ * better results for the user who performed undo. However, only the user who performed the undo
+ * will get the better results, the other users don't know which operations recreated a deleted
+ * range of content. There is more information in this ticket: https://github.com/yjs/yjs/issues/638
+ *
+ * @param {RelativePosition} rpos
+ * @param {Doc} doc
+ * @param {boolean} followUndoneDeletions - whether to follow undone deletions - see https://github.com/yjs/yjs/issues/638
+ * @return {AbsolutePosition|null}
+ *
+ * @function
+ */
+export const createAbsolutePositionFromRelativePosition = (rpos, doc, followUndoneDeletions = true) => {
+  const store = doc.store
+  const rightID = rpos.item
+  const typeID = rpos.type
+  const tname = rpos.tname
+  const assoc = rpos.assoc
+  let type = null
+  let index = 0
+  if (rightID !== null) {
+    if (getState(store, rightID.client) <= rightID.clock) {
+      return null
+    }
+    const res = followUndoneDeletions ? followRedone(store, rightID) : getItemWithOffset(store, rightID)
+    const right = res.item
+    if (!(right instanceof Item)) {
+      return null
+    }
+    type = /** @type {AbstractType<any>} */ (right.parent)
+    if (type._item === null || !type._item.deleted) {
+      index = (right.deleted || !right.countable) ? 0 : (res.diff + (assoc >= 0 ? 0 : 1)) // adjust position based on left association if necessary
+      let n = right.left
+      while (n !== null) {
+        if (!n.deleted && n.countable) {
+          index += n.length
+        }
+        n = n.left
+      }
+    }
+  } else {
+    if (tname !== null) {
+      type = doc.get(tname)
+    } else if (typeID !== null) {
+      if (getState(store, typeID.client) <= typeID.clock) {
+        // type does not exist yet
+        return null
+      }
+      const { item } = followUndoneDeletions ? followRedone(store, typeID) : { item: getItem(store, typeID) }
+      if (item instanceof Item && item.content instanceof ContentType) {
+        type = item.content.type
+      } else {
+        // struct is garbage collected
+        return null
+      }
+    } else {
+      throw error.unexpectedCase()
+    }
+    if (assoc >= 0) {
+      index = type._length
+    } else {
+      index = 0
+    }
+  }
+  return createAbsolutePosition(type, index, rpos.assoc)
+}
+
+/**
+ * @param {RelativePosition|null} a
+ * @param {RelativePosition|null} b
+ * @return {boolean}
+ *
+ * @function
+ */
+export const compareRelativePositions = (a, b) => a === b || (
+  a !== null && b !== null && a.tname === b.tname && compareIDs(a.item, b.item) && compareIDs(a.type, b.type) && a.assoc === b.assoc
+)
--- a/src/utils/Snapshot.js
+++ b/src/utils/Snapshot.js
@ -0,0 +1,236 @@
+import {
+  isDeleted,
+  createDeleteSetFromStructStore,
+  getStateVector,
+  getItemCleanStart,
+  iterateDeletedStructs,
+  writeDeleteSet,
+  writeStateVector,
+  readDeleteSet,
+  readStateVector,
+  createDeleteSet,
+  createID,
+  getState,
+  findIndexSS,
+  UpdateEncoderV2,
+  applyUpdateV2,
+  LazyStructReader,
+  equalDeleteSets,
+  UpdateDecoderV1, UpdateDecoderV2, DSEncoderV1, DSEncoderV2, DSDecoderV1, DSDecoderV2, Transaction, Doc, DeleteSet, Item, // eslint-disable-line
+  mergeDeleteSets
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as set from 'lib0/set'
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+
+export class Snapshot {
+  /**
+   * @param {DeleteSet} ds
+   * @param {Map<number,number>} sv state map
+   */
+  constructor (ds, sv) {
+    /**
+     * @type {DeleteSet}
+     */
+    this.ds = ds
+    /**
+     * State Map
+     * @type {Map<number,number>}
+     */
+    this.sv = sv
+  }
+}
+
+/**
+ * @param {Snapshot} snap1
+ * @param {Snapshot} snap2
+ * @return {boolean}
+ */
+export const equalSnapshots = (snap1, snap2) => {
+  const ds1 = snap1.ds.clients
+  const ds2 = snap2.ds.clients
+  const sv1 = snap1.sv
+  const sv2 = snap2.sv
+  if (sv1.size !== sv2.size || ds1.size !== ds2.size) {
+    return false
+  }
+  for (const [key, value] of sv1.entries()) {
+    if (sv2.get(key) !== value) {
+      return false
+    }
+  }
+  for (const [client, dsitems1] of ds1.entries()) {
+    const dsitems2 = ds2.get(client) || []
+    if (dsitems1.length !== dsitems2.length) {
+      return false
+    }
+    for (let i = 0; i < dsitems1.length; i++) {
+      const dsitem1 = dsitems1[i]
+      const dsitem2 = dsitems2[i]
+      if (dsitem1.clock !== dsitem2.clock || dsitem1.len !== dsitem2.len) {
+        return false
+      }
+    }
+  }
+  return true
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {DSEncoderV1 | DSEncoderV2} [encoder]
+ * @return {Uint8Array}
+ */
+export const encodeSnapshotV2 = (snapshot, encoder = new DSEncoderV2()) => {
+  writeDeleteSet(encoder, snapshot.ds)
+  writeStateVector(encoder, snapshot.sv)
+  return encoder.toUint8Array()
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @return {Uint8Array}
+ */
+export const encodeSnapshot = snapshot => encodeSnapshotV2(snapshot, new DSEncoderV1())
+
+/**
+ * @param {Uint8Array} buf
+ * @param {DSDecoderV1 | DSDecoderV2} [decoder]
+ * @return {Snapshot}
+ */
+export const decodeSnapshotV2 = (buf, decoder = new DSDecoderV2(decoding.createDecoder(buf))) => {
+  return new Snapshot(readDeleteSet(decoder), readStateVector(decoder))
+}
+
+/**
+ * @param {Uint8Array} buf
+ * @return {Snapshot}
+ */
+export const decodeSnapshot = buf => decodeSnapshotV2(buf, new DSDecoderV1(decoding.createDecoder(buf)))
+
+/**
+ * @param {DeleteSet} ds
+ * @param {Map<number,number>} sm
+ * @return {Snapshot}
+ */
+export const createSnapshot = (ds, sm) => new Snapshot(ds, sm)
+
+export const emptySnapshot = createSnapshot(createDeleteSet(), new Map())
+
+/**
+ * @param {Doc} doc
+ * @return {Snapshot}
+ */
+export const snapshot = doc => createSnapshot(createDeleteSetFromStructStore(doc.store), getStateVector(doc.store))
+
+/**
+ * @param {Item} item
+ * @param {Snapshot|undefined} snapshot
+ *
+ * @protected
+ * @function
+ */
+export const isVisible = (item, snapshot) => snapshot === undefined
+  ? !item.deleted
+  : snapshot.sv.has(item.id.client) && (snapshot.sv.get(item.id.client) || 0) > item.id.clock && !isDeleted(snapshot.ds, item.id)
+
+/**
+ * @param {Transaction} transaction
+ * @param {Snapshot} snapshot
+ */
+export const splitSnapshotAffectedStructs = (transaction, snapshot) => {
+  const meta = map.setIfUndefined(transaction.meta, splitSnapshotAffectedStructs, set.create)
+  const store = transaction.doc.store
+  // check if we already split for this snapshot
+  if (!meta.has(snapshot)) {
+    snapshot.sv.forEach((clock, client) => {
+      if (clock < getState(store, client)) {
+        getItemCleanStart(transaction, createID(client, clock))
+      }
+    })
+    iterateDeletedStructs(transaction, snapshot.ds, _item => {})
+    meta.add(snapshot)
+  }
+}
+
+/**
+ * @example
+ *  const ydoc = new Y.Doc({ gc: false })
+ *  ydoc.getText().insert(0, 'world!')
+ *  const snapshot = Y.snapshot(ydoc)
+ *  ydoc.getText().insert(0, 'hello ')
+ *  const restored = Y.createDocFromSnapshot(ydoc, snapshot)
+ *  assert(restored.getText().toString() === 'world!')
+ *
+ * @param {Doc} originDoc
+ * @param {Snapshot} snapshot
+ * @param {Doc} [newDoc] Optionally, you may define the Yjs document that receives the data from originDoc
+ * @return {Doc}
+ */
+export const createDocFromSnapshot = (originDoc, snapshot, newDoc = new Doc()) => {
+  if (originDoc.gc) {
+    // we should not try to restore a GC-ed document, because some of the restored items might have their content deleted
+    throw new Error('Garbage-collection must be disabled in `originDoc`!')
+  }
+  const { sv, ds } = snapshot
+
+  const encoder = new UpdateEncoderV2()
+  originDoc.transact(transaction => {
+    let size = 0
+    sv.forEach(clock => {
+      if (clock > 0) {
+        size++
+      }
+    })
+    encoding.writeVarUint(encoder.restEncoder, size)
+    // splitting the structs before writing them to the encoder
+    for (const [client, clock] of sv) {
+      if (clock === 0) {
+        continue
+      }
+      if (clock < getState(originDoc.store, client)) {
+        getItemCleanStart(transaction, createID(client, clock))
+      }
+      const structs = originDoc.store.clients.get(client) || []
+      const lastStructIndex = findIndexSS(structs, clock - 1)
+      // write # encoded structs
+      encoding.writeVarUint(encoder.restEncoder, lastStructIndex + 1)
+      encoder.writeClient(client)
+      // first clock written is 0
+      encoding.writeVarUint(encoder.restEncoder, 0)
+      for (let i = 0; i <= lastStructIndex; i++) {
+        structs[i].write(encoder, 0)
+      }
+    }
+    writeDeleteSet(encoder, ds)
+  })
+
+  applyUpdateV2(newDoc, encoder.toUint8Array(), 'snapshot')
+  return newDoc
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} [YDecoder]
+ */
+export const snapshotContainsUpdateV2 = (snapshot, update, YDecoder = UpdateDecoderV2) => {
+  const structs = []
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    structs.push(curr)
+    if ((snapshot.sv.get(curr.id.client) || 0) < curr.id.clock + curr.length) {
+      return false
+    }
+  }
+  const mergedDS = mergeDeleteSets([snapshot.ds, readDeleteSet(updateDecoder)])
+  return equalDeleteSets(snapshot.ds, mergedDS)
+}
+
+/**
+ * @param {Snapshot} snapshot
+ * @param {Uint8Array} update
+ */
+export const snapshotContainsUpdate = (snapshot, update) => snapshotContainsUpdateV2(snapshot, update, UpdateDecoderV1)
--- a/src/utils/StructStore.js
+++ b/src/utils/StructStore.js
@ -0,0 +1,261 @@
+import {
+  GC,
+  splitItem,
+  Transaction, ID, Item, DSDecoderV2 // eslint-disable-line
+} from '../internals.js'
+
+import * as math from 'lib0/math'
+import * as error from 'lib0/error'
+
+export class StructStore {
+  constructor () {
+    /**
+     * @type {Map<number,Array<GC|Item>>}
+     */
+    this.clients = new Map()
+    /**
+     * @type {null | { missing: Map<number, number>, update: Uint8Array }}
+     */
+    this.pendingStructs = null
+    /**
+     * @type {null | Uint8Array}
+     */
+    this.pendingDs = null
+  }
+}
+
+/**
+ * Return the states as a Map<client,clock>.
+ * Note that clock refers to the next expected clock id.
+ *
+ * @param {StructStore} store
+ * @return {Map<number,number>}
+ *
+ * @public
+ * @function
+ */
+export const getStateVector = store => {
+  const sm = new Map()
+  store.clients.forEach((structs, client) => {
+    const struct = structs[structs.length - 1]
+    sm.set(client, struct.id.clock + struct.length)
+  })
+  return sm
+}
+
+/**
+ * @param {StructStore} store
+ * @param {number} client
+ * @return {number}
+ *
+ * @public
+ * @function
+ */
+export const getState = (store, client) => {
+  const structs = store.clients.get(client)
+  if (structs === undefined) {
+    return 0
+  }
+  const lastStruct = structs[structs.length - 1]
+  return lastStruct.id.clock + lastStruct.length
+}
+
+/**
+ * @param {StructStore} store
+ *
+ * @private
+ * @function
+ */
+export const integrityCheck = 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 integrity check')
+      }
+    }
+  })
+}
+
+/**
+ * @param {StructStore} store
+ * @param {GC|Item} struct
+ *
+ * @private
+ * @function
+ */
+export const addStruct = (store, struct) => {
+  let structs = store.clients.get(struct.id.client)
+  if (structs === undefined) {
+    structs = []
+    store.clients.set(struct.id.client, structs)
+  } else {
+    const lastStruct = structs[structs.length - 1]
+    if (lastStruct.id.clock + lastStruct.length !== struct.id.clock) {
+      throw error.unexpectedCase()
+    }
+  }
+  structs.push(struct)
+}
+
+/**
+ * Perform a binary search on a sorted array
+ * @param {Array<Item|GC>} structs
+ * @param {number} clock
+ * @return {number}
+ *
+ * @private
+ * @function
+ */
+export const findIndexSS = (structs, clock) => {
+  let left = 0
+  let right = structs.length - 1
+  let mid = structs[right]
+  let midclock = mid.id.clock
+  if (midclock === clock) {
+    return right
+  }
+  // @todo does it even make sense to pivot the search?
+  // If a good split misses, it might actually increase the time to find the correct item.
+  // Currently, the only advantage is that search with pivoting might find the item on the first try.
+  let midindex = math.floor((clock / (midclock + mid.length - 1)) * right) // pivoting the search
+  while (left <= right) {
+    mid = structs[midindex]
+    midclock = mid.id.clock
+    if (midclock <= clock) {
+      if (clock < midclock + mid.length) {
+        return midindex
+      }
+      left = midindex + 1
+    } else {
+      right = midindex - 1
+    }
+    midindex = math.floor((left + right) / 2)
+  }
+  // Always check state before looking for a struct in StructStore
+  // Therefore the case of not finding a struct is unexpected
+  throw error.unexpectedCase()
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {GC|Item}
+ *
+ * @private
+ * @function
+ */
+export const find = (store, id) => {
+  /**
+   * @type {Array<GC|Item>}
+   */
+  // @ts-ignore
+  const structs = store.clients.get(id.client)
+  return structs[findIndexSS(structs, id.clock)]
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ * @private
+ * @function
+ */
+export const getItem = /** @type {function(StructStore,ID):Item} */ (find)
+
+/**
+ * @param {Transaction} transaction
+ * @param {Array<Item|GC>} structs
+ * @param {number} clock
+ */
+export const findIndexCleanStart = (transaction, structs, clock) => {
+  const index = findIndexSS(structs, clock)
+  const struct = structs[index]
+  if (struct.id.clock < clock && struct instanceof Item) {
+    structs.splice(index + 1, 0, splitItem(transaction, struct, clock - struct.id.clock))
+    return index + 1
+  }
+  return index
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {Transaction} transaction
+ * @param {ID} id
+ * @return {Item}
+ *
+ * @private
+ * @function
+ */
+export const getItemCleanStart = (transaction, id) => {
+  const structs = /** @type {Array<Item>} */ (transaction.doc.store.clients.get(id.client))
+  return structs[findIndexCleanStart(transaction, structs, id.clock)]
+}
+
+/**
+ * Expects that id is actually in store. This function throws or is an infinite loop otherwise.
+ *
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @param {ID} id
+ * @return {Item}
+ *
+ * @private
+ * @function
+ */
+export const getItemCleanEnd = (transaction, store, id) => {
+  /**
+   * @type {Array<Item>}
+   */
+  // @ts-ignore
+  const structs = store.clients.get(id.client)
+  const index = findIndexSS(structs, id.clock)
+  const struct = structs[index]
+  if (id.clock !== struct.id.clock + struct.length - 1 && struct.constructor !== GC) {
+    structs.splice(index + 1, 0, splitItem(transaction, struct, id.clock - struct.id.clock + 1))
+  }
+  return struct
+}
+
+/**
+ * Replace `item` with `newitem` in store
+ * @param {StructStore} store
+ * @param {GC|Item} struct
+ * @param {GC|Item} newStruct
+ *
+ * @private
+ * @function
+ */
+export const replaceStruct = (store, struct, newStruct) => {
+  const structs = /** @type {Array<GC|Item>} */ (store.clients.get(struct.id.client))
+  structs[findIndexSS(structs, struct.id.clock)] = newStruct
+}
+
+/**
+ * Iterate over a range of structs
+ *
+ * @param {Transaction} transaction
+ * @param {Array<Item|GC>} structs
+ * @param {number} clockStart Inclusive start
+ * @param {number} len
+ * @param {function(GC|Item):void} f
+ *
+ * @function
+ */
+export const iterateStructs = (transaction, structs, clockStart, len, f) => {
+  if (len === 0) {
+    return
+  }
+  const clockEnd = clockStart + len
+  let index = findIndexCleanStart(transaction, structs, clockStart)
+  let struct
+  do {
+    struct = structs[index++]
+    if (clockEnd < struct.id.clock + struct.length) {
+      findIndexCleanStart(transaction, structs, clockEnd)
+    }
+    f(struct)
+  } while (index < structs.length && structs[index].id.clock < clockEnd)
+}
--- a/src/utils/Transaction.js
+++ b/src/utils/Transaction.js
@ -0,0 +1,444 @@
+import {
+  getState,
+  writeStructsFromTransaction,
+  writeDeleteSet,
+  DeleteSet,
+  sortAndMergeDeleteSet,
+  getStateVector,
+  findIndexSS,
+  callEventHandlerListeners,
+  Item,
+  generateNewClientId,
+  createID,
+  cleanupYTextAfterTransaction,
+  UpdateEncoderV1, UpdateEncoderV2, GC, StructStore, AbstractType, AbstractStruct, YEvent, Doc // eslint-disable-line
+} from '../internals.js'
+
+import * as map from 'lib0/map'
+import * as math from 'lib0/math'
+import * as set from 'lib0/set'
+import * as logging from 'lib0/logging'
+import { callAll } from 'lib0/function'
+
+/**
+ * A transaction is created for every change on the Yjs model. It is possible
+ * to bundle changes on the Yjs model in a single transaction to
+ * minimize the number on messages sent and the number of observer calls.
+ * If possible the user of this library should bundle as many changes as
+ * possible. Here is an example to illustrate the advantages of bundling:
+ *
+ * @example
+ * const ydoc = new Y.Doc()
+ * const map = ydoc.getMap('map')
+ * // 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:
+ * ydoc.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<any>>,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<any>>,Array<YEvent<any>>>}
+     */
+    this.changedParentTypes = new Map()
+    /**
+     * @type {Array<AbstractStruct>}
+     */
+    this._mergeStructs = []
+    /**
+     * @type {any}
+     */
+    this.origin = origin
+    /**
+     * Stores meta information on the transaction
+     * @type {Map<any,any>}
+     */
+    this.meta = new Map()
+    /**
+     * Whether this change originates from this doc.
+     * @type {boolean}
+     */
+    this.local = local
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsAdded = new Set()
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsRemoved = new Set()
+    /**
+     * @type {Set<Doc>}
+     */
+    this.subdocsLoaded = new Set()
+    /**
+     * @type {boolean}
+     */
+    this._needFormattingCleanup = false
+  }
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Transaction} transaction
+ * @return {boolean} Whether data was written.
+ */
+export const writeUpdateMessageFromTransaction = (encoder, transaction) => {
+  if (transaction.deleteSet.clients.size === 0 && !map.any(transaction.afterState, (clock, client) => transaction.beforeState.get(client) !== clock)) {
+    return false
+  }
+  sortAndMergeDeleteSet(transaction.deleteSet)
+  writeStructsFromTransaction(encoder, transaction)
+  writeDeleteSet(encoder, transaction.deleteSet)
+  return true
+}
+
+/**
+ * @param {Transaction} transaction
+ *
+ * @private
+ * @function
+ */
+export const nextID = transaction => {
+  const y = transaction.doc
+  return createID(y.clientID, getState(y.store, y.clientID))
+}
+
+/**
+ * If `type.parent` was added in current transaction, `type` technically
+ * did not change, it was just added and we should not fire events for `type`.
+ *
+ * @param {Transaction} transaction
+ * @param {AbstractType<YEvent<any>>} 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
+ * @return {number} # of merged structs
+ */
+const tryToMergeWithLefts = (structs, pos) => {
+  let right = structs[pos]
+  let left = structs[pos - 1]
+  let i = pos
+  for (; i > 0; right = left, left = structs[--i - 1]) {
+    if (left.deleted === right.deleted && left.constructor === right.constructor) {
+      if (left.mergeWith(right)) {
+        if (right instanceof Item && right.parentSub !== null && /** @type {AbstractType<any>} */ (right.parent)._map.get(right.parentSub) === right) {
+          /** @type {AbstractType<any>} */ (right.parent)._map.set(right.parentSub, /** @type {Item} */ (left))
+        }
+        continue
+      }
+    }
+    break
+  }
+  const merged = pos - i
+  if (merged) {
+    // remove all merged structs from the array
+    structs.splice(pos + 1 - merged, merged)
+  }
+  return merged
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ * @param {function(Item):boolean} gcFilter
+ */
+const tryGcDeleteSet = (ds, store, gcFilter) => {
+  for (const [client, deleteItems] of ds.clients.entries()) {
+    const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+    for (let di = deleteItems.length - 1; di >= 0; di--) {
+      const deleteItem = deleteItems[di]
+      const endDeleteItemClock = deleteItem.clock + deleteItem.len
+      for (
+        let si = findIndexSS(structs, deleteItem.clock), struct = structs[si];
+        si < structs.length && struct.id.clock < endDeleteItemClock;
+        struct = structs[++si]
+      ) {
+        const struct = structs[si]
+        if (deleteItem.clock + deleteItem.len <= struct.id.clock) {
+          break
+        }
+        if (struct instanceof Item && struct.deleted && !struct.keep && gcFilter(struct)) {
+          struct.gc(store, false)
+        }
+      }
+    }
+  }
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ */
+const tryMergeDeleteSet = (ds, store) => {
+  // try to merge deleted / gc'd items
+  // merge from right to left for better efficiency and so we don't miss any merge targets
+  ds.clients.forEach((deleteItems, client) => {
+    const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+    for (let di = deleteItems.length - 1; di >= 0; di--) {
+      const deleteItem = deleteItems[di]
+      // start with merging the item next to the last deleted item
+      const mostRightIndexToCheck = math.min(structs.length - 1, 1 + findIndexSS(structs, deleteItem.clock + deleteItem.len - 1))
+      for (
+        let si = mostRightIndexToCheck, struct = structs[si];
+        si > 0 && struct.id.clock >= deleteItem.clock;
+        struct = structs[si]
+      ) {
+        si -= 1 + tryToMergeWithLefts(structs, si)
+      }
+    }
+  })
+}
+
+/**
+ * @param {DeleteSet} ds
+ * @param {StructStore} store
+ * @param {function(Item):boolean} gcFilter
+ */
+export const tryGc = (ds, store, gcFilter) => {
+  tryGcDeleteSet(ds, store, gcFilter)
+  tryMergeDeleteSet(ds, store)
+}
+
+/**
+ * @param {Array<Transaction>} transactionCleanups
+ * @param {number} i
+ */
+const cleanupTransactions = (transactionCleanups, i) => {
+  if (i < transactionCleanups.length) {
+    const transaction = transactionCleanups[i]
+    const doc = transaction.doc
+    const store = doc.store
+    const ds = transaction.deleteSet
+    const mergeStructs = transaction._mergeStructs
+    try {
+      sortAndMergeDeleteSet(ds)
+      transaction.afterState = getStateVector(transaction.doc.store)
+      doc.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) => {
+          // We need to think about the possibility that the user transforms the
+          // Y.Doc in the event.
+          if (type._dEH.l.length > 0 && (type._item === null || !type._item.deleted)) {
+            events = events
+              .filter(event =>
+                event.target._item === null || !event.target._item.deleted
+              )
+            events
+              .forEach(event => {
+                event.currentTarget = type
+                // path is relative to the current target
+                event._path = null
+              })
+            // sort events by path length so that top-level events are fired first.
+            events
+              .sort((event1, event2) => event1.path.length - event2.path.length)
+            // We don't need to check for events.length
+            // because we know it has at least one element
+            callEventHandlerListeners(type._dEH, events, transaction)
+          }
+        })
+      })
+      fs.push(() => doc.emit('afterTransaction', [transaction, doc]))
+      callAll(fs, [])
+      if (transaction._needFormattingCleanup) {
+        cleanupYTextAfterTransaction(transaction)
+      }
+    } finally {
+      // Replace deleted items with ItemDeleted / GC.
+      // This is where content is actually remove from the Yjs Doc.
+      if (doc.gc) {
+        tryGcDeleteSet(ds, store, doc.gcFilter)
+      }
+      tryMergeDeleteSet(ds, store)
+
+      // on all affected store.clients props, try to merge
+      transaction.afterState.forEach((clock, client) => {
+        const beforeClock = transaction.beforeState.get(client) || 0
+        if (beforeClock !== clock) {
+          const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+          // we iterate from right to left so we can safely remove entries
+          const firstChangePos = math.max(findIndexSS(structs, beforeClock), 1)
+          for (let i = structs.length - 1; i >= firstChangePos;) {
+            i -= 1 + tryToMergeWithLefts(structs, i)
+          }
+        }
+      })
+      // try to merge mergeStructs
+      // @todo: it makes more sense to transform mergeStructs to a DS, sort it, and merge from right to left
+      //        but at the moment DS does not handle duplicates
+      for (let i = mergeStructs.length - 1; i >= 0; i--) {
+        const { client, clock } = mergeStructs[i].id
+        const structs = /** @type {Array<GC|Item>} */ (store.clients.get(client))
+        const replacedStructPos = findIndexSS(structs, clock)
+        if (replacedStructPos + 1 < structs.length) {
+          if (tryToMergeWithLefts(structs, replacedStructPos + 1) > 1) {
+            continue // no need to perform next check, both are already merged
+          }
+        }
+        if (replacedStructPos > 0) {
+          tryToMergeWithLefts(structs, replacedStructPos)
+        }
+      }
+      if (!transaction.local && transaction.afterState.get(doc.clientID) !== transaction.beforeState.get(doc.clientID)) {
+        logging.print(logging.ORANGE, logging.BOLD, '[yjs] ', logging.UNBOLD, logging.RED, 'Changed the client-id because another client seems to be using it.')
+        doc.clientID = generateNewClientId()
+      }
+      // @todo Merge all the transactions into one and provide send the data as a single update message
+      doc.emit('afterTransactionCleanup', [transaction, doc])
+      if (doc._observers.has('update')) {
+        const encoder = new UpdateEncoderV1()
+        const hasContent = writeUpdateMessageFromTransaction(encoder, transaction)
+        if (hasContent) {
+          doc.emit('update', [encoder.toUint8Array(), transaction.origin, doc, transaction])
+        }
+      }
+      if (doc._observers.has('updateV2')) {
+        const encoder = new UpdateEncoderV2()
+        const hasContent = writeUpdateMessageFromTransaction(encoder, transaction)
+        if (hasContent) {
+          doc.emit('updateV2', [encoder.toUint8Array(), transaction.origin, doc, transaction])
+        }
+      }
+      const { subdocsAdded, subdocsLoaded, subdocsRemoved } = transaction
+      if (subdocsAdded.size > 0 || subdocsRemoved.size > 0 || subdocsLoaded.size > 0) {
+        subdocsAdded.forEach(subdoc => {
+          subdoc.clientID = doc.clientID
+          if (subdoc.collectionid == null) {
+            subdoc.collectionid = doc.collectionid
+          }
+          doc.subdocs.add(subdoc)
+        })
+        subdocsRemoved.forEach(subdoc => doc.subdocs.delete(subdoc))
+        doc.emit('subdocs', [{ loaded: subdocsLoaded, added: subdocsAdded, removed: subdocsRemoved }, doc, transaction])
+        subdocsRemoved.forEach(subdoc => subdoc.destroy())
+      }
+
+      if (transactionCleanups.length <= i + 1) {
+        doc._transactionCleanups = []
+        doc.emit('afterAllTransactions', [doc, transactionCleanups])
+      } else {
+        cleanupTransactions(transactionCleanups, i + 1)
+      }
+    }
+  }
+}
+
+/**
+ * Implements the functionality of `y.transact(()=>{..})`
+ *
+ * @template T
+ * @param {Doc} doc
+ * @param {function(Transaction):T} f
+ * @param {any} [origin=true]
+ * @return {T}
+ *
+ * @function
+ */
+export const transact = (doc, f, origin = null, local = true) => {
+  const transactionCleanups = doc._transactionCleanups
+  let initialCall = false
+  /**
+   * @type {any}
+   */
+  let result = null
+  if (doc._transaction === null) {
+    initialCall = true
+    doc._transaction = new Transaction(doc, origin, local)
+    transactionCleanups.push(doc._transaction)
+    if (transactionCleanups.length === 1) {
+      doc.emit('beforeAllTransactions', [doc])
+    }
+    doc.emit('beforeTransaction', [doc._transaction, doc])
+  }
+  try {
+    result = f(doc._transaction)
+  } finally {
+    if (initialCall) {
+      const finishCleanup = doc._transaction === transactionCleanups[0]
+      doc._transaction = null
+      if (finishCleanup) {
+        // 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)
+      }
+    }
+  }
+  return result
+}
--- a/src/utils/UndoManager.js
+++ b/src/utils/UndoManager.js
@ -0,0 +1,400 @@
+import {
+  mergeDeleteSets,
+  iterateDeletedStructs,
+  keepItem,
+  transact,
+  createID,
+  redoItem,
+  isParentOf,
+  followRedone,
+  getItemCleanStart,
+  isDeleted,
+  addToDeleteSet,
+  YEvent, Transaction, Doc, Item, GC, DeleteSet, AbstractType // eslint-disable-line
+} from '../internals.js'
+
+import * as time from 'lib0/time'
+import * as array from 'lib0/array'
+import * as logging from 'lib0/logging'
+import { ObservableV2 } from 'lib0/observable'
+
+export class StackItem {
+  /**
+   * @param {DeleteSet} deletions
+   * @param {DeleteSet} insertions
+   */
+  constructor (deletions, insertions) {
+    this.insertions = insertions
+    this.deletions = deletions
+    /**
+     * Use this to save and restore metadata like selection range
+     */
+    this.meta = new Map()
+  }
+}
+/**
+ * @param {Transaction} tr
+ * @param {UndoManager} um
+ * @param {StackItem} stackItem
+ */
+const clearUndoManagerStackItem = (tr, um, stackItem) => {
+  iterateDeletedStructs(tr, stackItem.deletions, item => {
+    if (item instanceof Item && um.scope.some(type => type === tr.doc || isParentOf(/** @type {AbstractType<any>} */ (type), item))) {
+      keepItem(item, false)
+    }
+  })
+}
+
+/**
+ * @param {UndoManager} undoManager
+ * @param {Array<StackItem>} stack
+ * @param {'undo'|'redo'} eventType
+ * @return {StackItem?}
+ */
+const popStackItem = (undoManager, stack, eventType) => {
+  /**
+   * Keep a reference to the transaction so we can fire the event with the changedParentTypes
+   * @type {any}
+   */
+  let _tr = null
+  const doc = undoManager.doc
+  const scope = undoManager.scope
+  transact(doc, transaction => {
+    while (stack.length > 0 && undoManager.currStackItem === null) {
+      const store = doc.store
+      const stackItem = /** @type {StackItem} */ (stack.pop())
+      /**
+       * @type {Set<Item>}
+       */
+      const itemsToRedo = new Set()
+      /**
+       * @type {Array<Item>}
+       */
+      const itemsToDelete = []
+      let performedChange = false
+      iterateDeletedStructs(transaction, stackItem.insertions, struct => {
+        if (struct instanceof Item) {
+          if (struct.redone !== null) {
+            let { item, diff } = followRedone(store, struct.id)
+            if (diff > 0) {
+              item = getItemCleanStart(transaction, createID(item.id.client, item.id.clock + diff))
+            }
+            struct = item
+          }
+          if (!struct.deleted && scope.some(type => type === transaction.doc || isParentOf(/** @type {AbstractType<any>} */ (type), /** @type {Item} */ (struct)))) {
+            itemsToDelete.push(struct)
+          }
+        }
+      })
+      iterateDeletedStructs(transaction, stackItem.deletions, struct => {
+        if (
+          struct instanceof Item &&
+          scope.some(type => type === transaction.doc || isParentOf(/** @type {AbstractType<any>} */ (type), struct)) &&
+          // Never redo structs in stackItem.insertions because they were created and deleted in the same capture interval.
+          !isDeleted(stackItem.insertions, struct.id)
+        ) {
+          itemsToRedo.add(struct)
+        }
+      })
+      itemsToRedo.forEach(struct => {
+        performedChange = redoItem(transaction, struct, itemsToRedo, stackItem.insertions, undoManager.ignoreRemoteMapChanges, undoManager) !== null || performedChange
+      })
+      // We want to delete in reverse order so that children are deleted before
+      // parents, so we have more information available when items are filtered.
+      for (let i = itemsToDelete.length - 1; i >= 0; i--) {
+        const item = itemsToDelete[i]
+        if (undoManager.deleteFilter(item)) {
+          item.delete(transaction)
+          performedChange = true
+        }
+      }
+      undoManager.currStackItem = performedChange ? stackItem : null
+    }
+    transaction.changed.forEach((subProps, type) => {
+      // destroy search marker if necessary
+      if (subProps.has(null) && type._searchMarker) {
+        type._searchMarker.length = 0
+      }
+    })
+    _tr = transaction
+  }, undoManager)
+  const res = undoManager.currStackItem
+  if (res != null) {
+    const changedParentTypes = _tr.changedParentTypes
+    undoManager.emit('stack-item-popped', [{ stackItem: res, type: eventType, changedParentTypes, origin: undoManager }, undoManager])
+    undoManager.currStackItem = null
+  }
+  return res
+}
+
+/**
+ * @typedef {Object} UndoManagerOptions
+ * @property {number} [UndoManagerOptions.captureTimeout=500]
+ * @property {function(Transaction):boolean} [UndoManagerOptions.captureTransaction] Do not capture changes of a Transaction if result false.
+ * @property {function(Item):boolean} [UndoManagerOptions.deleteFilter=()=>true] Sometimes
+ * it is necessary to filter what 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])]
+ * @property {boolean} [ignoreRemoteMapChanges] Experimental. By default, the UndoManager will never overwrite remote changes. Enable this property to enable overwriting remote changes on key-value changes (Y.Map, properties on Y.Xml, etc..).
+ * @property {Doc} [doc] The document that this UndoManager operates on. Only needed if typeScope is empty.
+ */
+
+/**
+ * @typedef {Object} StackItemEvent
+ * @property {StackItem} StackItemEvent.stackItem
+ * @property {any} StackItemEvent.origin
+ * @property {'undo'|'redo'} StackItemEvent.type
+ * @property {Map<AbstractType<YEvent<any>>,Array<YEvent<any>>>} StackItemEvent.changedParentTypes
+ */
+
+/**
+ * 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 {ObservableV2<{'stack-item-added':function(StackItemEvent, UndoManager):void, 'stack-item-popped': function(StackItemEvent, UndoManager):void, 'stack-cleared': function({ undoStackCleared: boolean, redoStackCleared: boolean }):void, 'stack-item-updated': function(StackItemEvent, UndoManager):void }>}
+ */
+export class UndoManager extends ObservableV2 {
+  /**
+   * @param {Doc|AbstractType<any>|Array<AbstractType<any>>} typeScope Limits the scope of the UndoManager. If this is set to a ydoc instance, all changes on that ydoc will be undone. If set to a specific type, only changes on that type or its children will be undone. Also accepts an array of types.
+   * @param {UndoManagerOptions} options
+   */
+  constructor (typeScope, {
+    captureTimeout = 500,
+    captureTransaction = _tr => true,
+    deleteFilter = () => true,
+    trackedOrigins = new Set([null]),
+    ignoreRemoteMapChanges = false,
+    doc = /** @type {Doc} */ (array.isArray(typeScope) ? typeScope[0].doc : typeScope instanceof Doc ? typeScope : typeScope.doc)
+  } = {}) {
+    super()
+    /**
+     * @type {Array<AbstractType<any> | Doc>}
+     */
+    this.scope = []
+    this.doc = doc
+    this.addToScope(typeScope)
+    this.deleteFilter = deleteFilter
+    trackedOrigins.add(this)
+    this.trackedOrigins = trackedOrigins
+    this.captureTransaction = captureTransaction
+    /**
+     * @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
+    /**
+     * The currently popped stack item if UndoManager.undoing or UndoManager.redoing
+     *
+     * @type {StackItem|null}
+     */
+    this.currStackItem = null
+    this.lastChange = 0
+    this.ignoreRemoteMapChanges = ignoreRemoteMapChanges
+    this.captureTimeout = captureTimeout
+    /**
+     * @param {Transaction} transaction
+     */
+    this.afterTransactionHandler = transaction => {
+      // Only track certain transactions
+      if (
+        !this.captureTransaction(transaction) ||
+        !this.scope.some(type => transaction.changedParentTypes.has(/** @type {AbstractType<any>} */ (type)) || type === this.doc) ||
+        (!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.clear(false, true)
+      }
+      const insertions = new DeleteSet()
+      transaction.afterState.forEach((endClock, client) => {
+        const startClock = transaction.beforeState.get(client) || 0
+        const len = endClock - startClock
+        if (len > 0) {
+          addToDeleteSet(insertions, client, startClock, len)
+        }
+      })
+      const now = time.getUnixTime()
+      let didAdd = false
+      if (this.lastChange > 0 && now - this.lastChange < this.captureTimeout && stack.length > 0 && !undoing && !redoing) {
+        // append change to last stack op
+        const lastOp = stack[stack.length - 1]
+        lastOp.deletions = mergeDeleteSets([lastOp.deletions, transaction.deleteSet])
+        lastOp.insertions = mergeDeleteSets([lastOp.insertions, insertions])
+      } else {
+        // create a new stack op
+        stack.push(new StackItem(transaction.deleteSet, insertions))
+        didAdd = true
+      }
+      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 => type === transaction.doc || isParentOf(/** @type {AbstractType<any>} */ (type), item))) {
+          keepItem(item, true)
+        }
+      })
+      /**
+       * @type {[StackItemEvent, UndoManager]}
+       */
+      const changeEvent = [{ stackItem: stack[stack.length - 1], origin: transaction.origin, type: undoing ? 'redo' : 'undo', changedParentTypes: transaction.changedParentTypes }, this]
+      if (didAdd) {
+        this.emit('stack-item-added', changeEvent)
+      } else {
+        this.emit('stack-item-updated', changeEvent)
+      }
+    }
+    this.doc.on('afterTransaction', this.afterTransactionHandler)
+    this.doc.on('destroy', () => {
+      this.destroy()
+    })
+  }
+
+  /**
+   * Extend the scope.
+   *
+   * @param {Array<AbstractType<any> | Doc> | AbstractType<any> | Doc} ytypes
+   */
+  addToScope (ytypes) {
+    const tmpSet = new Set(this.scope)
+    ytypes = array.isArray(ytypes) ? ytypes : [ytypes]
+    ytypes.forEach(ytype => {
+      if (!tmpSet.has(ytype)) {
+        tmpSet.add(ytype)
+        if (ytype instanceof AbstractType ? ytype.doc !== this.doc : ytype !== this.doc) logging.warn('[yjs#509] Not same Y.Doc') // use MultiDocUndoManager instead. also see https://github.com/yjs/yjs/issues/509
+        this.scope.push(ytype)
+      }
+    })
+  }
+
+  /**
+   * @param {any} origin
+   */
+  addTrackedOrigin (origin) {
+    this.trackedOrigins.add(origin)
+  }
+
+  /**
+   * @param {any} origin
+   */
+  removeTrackedOrigin (origin) {
+    this.trackedOrigins.delete(origin)
+  }
+
+  clear (clearUndoStack = true, clearRedoStack = true) {
+    if ((clearUndoStack && this.canUndo()) || (clearRedoStack && this.canRedo())) {
+      this.doc.transact(tr => {
+        if (clearUndoStack) {
+          this.undoStack.forEach(item => clearUndoManagerStackItem(tr, this, item))
+          this.undoStack = []
+        }
+        if (clearRedoStack) {
+          this.redoStack.forEach(item => clearUndoManagerStackItem(tr, this, item))
+          this.redoStack = []
+        }
+        this.emit('stack-cleared', [{ undoStackCleared: clearUndoStack, redoStackCleared: clearRedoStack }])
+      })
+    }
+  }
+
+  /**
+   * 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
+  }
+
+  /**
+   * Are undo steps available?
+   *
+   * @return {boolean} `true` if undo is possible
+   */
+  canUndo () {
+    return this.undoStack.length > 0
+  }
+
+  /**
+   * Are redo steps available?
+   *
+   * @return {boolean} `true` if redo is possible
+   */
+  canRedo () {
+    return this.redoStack.length > 0
+  }
+
+  destroy () {
+    this.trackedOrigins.delete(this)
+    this.doc.off('afterTransaction', this.afterTransactionHandler)
+    super.destroy()
+  }
+}
--- a/src/utils/UpdateDecoder.js
+++ b/src/utils/UpdateDecoder.js
@ -0,0 +1,281 @@
+import * as buffer from 'lib0/buffer'
+import * as decoding from 'lib0/decoding'
+import {
+  ID, createID
+} from '../internals.js'
+
+export class DSDecoderV1 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    this.restDecoder = decoder
+  }
+
+  resetDsCurVal () {
+    // nop
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsClock () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsLen () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+}
+
+export class UpdateDecoderV1 extends DSDecoderV1 {
+  /**
+   * @return {ID}
+   */
+  readLeftID () {
+    return createID(decoding.readVarUint(this.restDecoder), decoding.readVarUint(this.restDecoder))
+  }
+
+  /**
+   * @return {ID}
+   */
+  readRightID () {
+    return createID(decoding.readVarUint(this.restDecoder), decoding.readVarUint(this.restDecoder))
+  }
+
+  /**
+   * Read the next client id.
+   * Use this in favor of readID whenever possible to reduce the number of objects created.
+   */
+  readClient () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readInfo () {
+    return decoding.readUint8(this.restDecoder)
+  }
+
+  /**
+   * @return {string}
+   */
+  readString () {
+    return decoding.readVarString(this.restDecoder)
+  }
+
+  /**
+   * @return {boolean} isKey
+   */
+  readParentInfo () {
+    return decoding.readVarUint(this.restDecoder) === 1
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readTypeRef () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @return {number} len
+   */
+  readLen () {
+    return decoding.readVarUint(this.restDecoder)
+  }
+
+  /**
+   * @return {any}
+   */
+  readAny () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {Uint8Array}
+   */
+  readBuf () {
+    return buffer.copyUint8Array(decoding.readVarUint8Array(this.restDecoder))
+  }
+
+  /**
+   * Legacy implementation uses JSON parse. We use any-decoding in v2.
+   *
+   * @return {any}
+   */
+  readJSON () {
+    return JSON.parse(decoding.readVarString(this.restDecoder))
+  }
+
+  /**
+   * @return {string}
+   */
+  readKey () {
+    return decoding.readVarString(this.restDecoder)
+  }
+}
+
+export class DSDecoderV2 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    /**
+     * @private
+     */
+    this.dsCurrVal = 0
+    this.restDecoder = decoder
+  }
+
+  resetDsCurVal () {
+    this.dsCurrVal = 0
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsClock () {
+    this.dsCurrVal += decoding.readVarUint(this.restDecoder)
+    return this.dsCurrVal
+  }
+
+  /**
+   * @return {number}
+   */
+  readDsLen () {
+    const diff = decoding.readVarUint(this.restDecoder) + 1
+    this.dsCurrVal += diff
+    return diff
+  }
+}
+
+export class UpdateDecoderV2 extends DSDecoderV2 {
+  /**
+   * @param {decoding.Decoder} decoder
+   */
+  constructor (decoder) {
+    super(decoder)
+    /**
+     * List of cached keys. If the keys[id] does not exist, we read a new key
+     * from stringEncoder and push it to keys.
+     *
+     * @type {Array<string>}
+     */
+    this.keys = []
+    decoding.readVarUint(decoder) // read feature flag - currently unused
+    this.keyClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.clientDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.leftClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.rightClockDecoder = new decoding.IntDiffOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.infoDecoder = new decoding.RleDecoder(decoding.readVarUint8Array(decoder), decoding.readUint8)
+    this.stringDecoder = new decoding.StringDecoder(decoding.readVarUint8Array(decoder))
+    this.parentInfoDecoder = new decoding.RleDecoder(decoding.readVarUint8Array(decoder), decoding.readUint8)
+    this.typeRefDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+    this.lenDecoder = new decoding.UintOptRleDecoder(decoding.readVarUint8Array(decoder))
+  }
+
+  /**
+   * @return {ID}
+   */
+  readLeftID () {
+    return new ID(this.clientDecoder.read(), this.leftClockDecoder.read())
+  }
+
+  /**
+   * @return {ID}
+   */
+  readRightID () {
+    return new ID(this.clientDecoder.read(), this.rightClockDecoder.read())
+  }
+
+  /**
+   * Read the next client id.
+   * Use this in favor of readID whenever possible to reduce the number of objects created.
+   */
+  readClient () {
+    return this.clientDecoder.read()
+  }
+
+  /**
+   * @return {number} info An unsigned 8-bit integer
+   */
+  readInfo () {
+    return /** @type {number} */ (this.infoDecoder.read())
+  }
+
+  /**
+   * @return {string}
+   */
+  readString () {
+    return this.stringDecoder.read()
+  }
+
+  /**
+   * @return {boolean}
+   */
+  readParentInfo () {
+    return this.parentInfoDecoder.read() === 1
+  }
+
+  /**
+   * @return {number} An unsigned 8-bit integer
+   */
+  readTypeRef () {
+    return this.typeRefDecoder.read()
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @return {number}
+   */
+  readLen () {
+    return this.lenDecoder.read()
+  }
+
+  /**
+   * @return {any}
+   */
+  readAny () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {Uint8Array}
+   */
+  readBuf () {
+    return decoding.readVarUint8Array(this.restDecoder)
+  }
+
+  /**
+   * This is mainly here for legacy purposes.
+   *
+   * Initial we incoded objects using JSON. Now we use the much faster lib0/any-encoder. This method mainly exists for legacy purposes for the v1 encoder.
+   *
+   * @return {any}
+   */
+  readJSON () {
+    return decoding.readAny(this.restDecoder)
+  }
+
+  /**
+   * @return {string}
+   */
+  readKey () {
+    const keyClock = this.keyClockDecoder.read()
+    if (keyClock < this.keys.length) {
+      return this.keys[keyClock]
+    } else {
+      const key = this.stringDecoder.read()
+      this.keys.push(key)
+      return key
+    }
+  }
+}
--- a/src/utils/UpdateEncoder.js
+++ b/src/utils/UpdateEncoder.js
@ -0,0 +1,320 @@
+import * as error from 'lib0/error'
+import * as encoding from 'lib0/encoding'
+
+import {
+  ID // eslint-disable-line
+} from '../internals.js'
+
+export class DSEncoderV1 {
+  constructor () {
+    this.restEncoder = encoding.createEncoder()
+  }
+
+  toUint8Array () {
+    return encoding.toUint8Array(this.restEncoder)
+  }
+
+  resetDsCurVal () {
+    // nop
+  }
+
+  /**
+   * @param {number} clock
+   */
+  writeDsClock (clock) {
+    encoding.writeVarUint(this.restEncoder, clock)
+  }
+
+  /**
+   * @param {number} len
+   */
+  writeDsLen (len) {
+    encoding.writeVarUint(this.restEncoder, len)
+  }
+}
+
+export class UpdateEncoderV1 extends DSEncoderV1 {
+  /**
+   * @param {ID} id
+   */
+  writeLeftID (id) {
+    encoding.writeVarUint(this.restEncoder, id.client)
+    encoding.writeVarUint(this.restEncoder, id.clock)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeRightID (id) {
+    encoding.writeVarUint(this.restEncoder, id.client)
+    encoding.writeVarUint(this.restEncoder, id.clock)
+  }
+
+  /**
+   * Use writeClient and writeClock instead of writeID if possible.
+   * @param {number} client
+   */
+  writeClient (client) {
+    encoding.writeVarUint(this.restEncoder, client)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeInfo (info) {
+    encoding.writeUint8(this.restEncoder, info)
+  }
+
+  /**
+   * @param {string} s
+   */
+  writeString (s) {
+    encoding.writeVarString(this.restEncoder, s)
+  }
+
+  /**
+   * @param {boolean} isYKey
+   */
+  writeParentInfo (isYKey) {
+    encoding.writeVarUint(this.restEncoder, isYKey ? 1 : 0)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeTypeRef (info) {
+    encoding.writeVarUint(this.restEncoder, info)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @param {number} len
+   */
+  writeLen (len) {
+    encoding.writeVarUint(this.restEncoder, len)
+  }
+
+  /**
+   * @param {any} any
+   */
+  writeAny (any) {
+    encoding.writeAny(this.restEncoder, any)
+  }
+
+  /**
+   * @param {Uint8Array} buf
+   */
+  writeBuf (buf) {
+    encoding.writeVarUint8Array(this.restEncoder, buf)
+  }
+
+  /**
+   * @param {any} embed
+   */
+  writeJSON (embed) {
+    encoding.writeVarString(this.restEncoder, JSON.stringify(embed))
+  }
+
+  /**
+   * @param {string} key
+   */
+  writeKey (key) {
+    encoding.writeVarString(this.restEncoder, key)
+  }
+}
+
+export class DSEncoderV2 {
+  constructor () {
+    this.restEncoder = encoding.createEncoder() // encodes all the rest / non-optimized
+    this.dsCurrVal = 0
+  }
+
+  toUint8Array () {
+    return encoding.toUint8Array(this.restEncoder)
+  }
+
+  resetDsCurVal () {
+    this.dsCurrVal = 0
+  }
+
+  /**
+   * @param {number} clock
+   */
+  writeDsClock (clock) {
+    const diff = clock - this.dsCurrVal
+    this.dsCurrVal = clock
+    encoding.writeVarUint(this.restEncoder, diff)
+  }
+
+  /**
+   * @param {number} len
+   */
+  writeDsLen (len) {
+    if (len === 0) {
+      error.unexpectedCase()
+    }
+    encoding.writeVarUint(this.restEncoder, len - 1)
+    this.dsCurrVal += len
+  }
+}
+
+export class UpdateEncoderV2 extends DSEncoderV2 {
+  constructor () {
+    super()
+    /**
+     * @type {Map<string,number>}
+     */
+    this.keyMap = new Map()
+    /**
+     * Refers to the next unique key-identifier to me used.
+     * See writeKey method for more information.
+     *
+     * @type {number}
+     */
+    this.keyClock = 0
+    this.keyClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.clientEncoder = new encoding.UintOptRleEncoder()
+    this.leftClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.rightClockEncoder = new encoding.IntDiffOptRleEncoder()
+    this.infoEncoder = new encoding.RleEncoder(encoding.writeUint8)
+    this.stringEncoder = new encoding.StringEncoder()
+    this.parentInfoEncoder = new encoding.RleEncoder(encoding.writeUint8)
+    this.typeRefEncoder = new encoding.UintOptRleEncoder()
+    this.lenEncoder = new encoding.UintOptRleEncoder()
+  }
+
+  toUint8Array () {
+    const encoder = encoding.createEncoder()
+    encoding.writeVarUint(encoder, 0) // this is a feature flag that we might use in the future
+    encoding.writeVarUint8Array(encoder, this.keyClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.clientEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.leftClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.rightClockEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, encoding.toUint8Array(this.infoEncoder))
+    encoding.writeVarUint8Array(encoder, this.stringEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, encoding.toUint8Array(this.parentInfoEncoder))
+    encoding.writeVarUint8Array(encoder, this.typeRefEncoder.toUint8Array())
+    encoding.writeVarUint8Array(encoder, this.lenEncoder.toUint8Array())
+    // @note The rest encoder is appended! (note the missing var)
+    encoding.writeUint8Array(encoder, encoding.toUint8Array(this.restEncoder))
+    return encoding.toUint8Array(encoder)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeLeftID (id) {
+    this.clientEncoder.write(id.client)
+    this.leftClockEncoder.write(id.clock)
+  }
+
+  /**
+   * @param {ID} id
+   */
+  writeRightID (id) {
+    this.clientEncoder.write(id.client)
+    this.rightClockEncoder.write(id.clock)
+  }
+
+  /**
+   * @param {number} client
+   */
+  writeClient (client) {
+    this.clientEncoder.write(client)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeInfo (info) {
+    this.infoEncoder.write(info)
+  }
+
+  /**
+   * @param {string} s
+   */
+  writeString (s) {
+    this.stringEncoder.write(s)
+  }
+
+  /**
+   * @param {boolean} isYKey
+   */
+  writeParentInfo (isYKey) {
+    this.parentInfoEncoder.write(isYKey ? 1 : 0)
+  }
+
+  /**
+   * @param {number} info An unsigned 8-bit integer
+   */
+  writeTypeRef (info) {
+    this.typeRefEncoder.write(info)
+  }
+
+  /**
+   * Write len of a struct - well suited for Opt RLE encoder.
+   *
+   * @param {number} len
+   */
+  writeLen (len) {
+    this.lenEncoder.write(len)
+  }
+
+  /**
+   * @param {any} any
+   */
+  writeAny (any) {
+    encoding.writeAny(this.restEncoder, any)
+  }
+
+  /**
+   * @param {Uint8Array} buf
+   */
+  writeBuf (buf) {
+    encoding.writeVarUint8Array(this.restEncoder, buf)
+  }
+
+  /**
+   * This is mainly here for legacy purposes.
+   *
+   * Initial we incoded objects using JSON. Now we use the much faster lib0/any-encoder. This method mainly exists for legacy purposes for the v1 encoder.
+   *
+   * @param {any} embed
+   */
+  writeJSON (embed) {
+    encoding.writeAny(this.restEncoder, embed)
+  }
+
+  /**
+   * Property keys are often reused. For example, in y-prosemirror the key `bold` might
+   * occur very often. For a 3d application, the key `position` might occur very often.
+   *
+   * We cache these keys in a Map and refer to them via a unique number.
+   *
+   * @param {string} key
+   */
+  writeKey (key) {
+    const clock = this.keyMap.get(key)
+    if (clock === undefined) {
+      /**
+       * @todo uncomment to introduce this feature finally
+       *
+       * Background. The ContentFormat object was always encoded using writeKey, but the decoder used to use readString.
+       * Furthermore, I forgot to set the keyclock. So everything was working fine.
+       *
+       * However, this feature here is basically useless as it is not being used (it actually only consumes extra memory).
+       *
+       * I don't know yet how to reintroduce this feature..
+       *
+       * Older clients won't be able to read updates when we reintroduce this feature. So this should probably be done using a flag.
+       *
+       */
+      // this.keyMap.set(key, this.keyClock)
+      this.keyClockEncoder.write(this.keyClock++)
+      this.stringEncoder.write(key)
+    } else {
+      this.keyClockEncoder.write(clock)
+    }
+  }
+}
--- a/src/utils/YEvent.js
+++ b/src/utils/YEvent.js
@ -0,0 +1,277 @@
+import {
+  isDeleted,
+  Item, AbstractType, Transaction, AbstractStruct // eslint-disable-line
+} from '../internals.js'
+
+import * as set from 'lib0/set'
+import * as array from 'lib0/array'
+import * as error from 'lib0/error'
+
+const errorComputeChanges = 'You must not compute changes after the event-handler fired.'
+
+/**
+ * @template {AbstractType<any>} T
+ * YEvent describes the changes on a YType.
+ */
+export class YEvent {
+  /**
+   * @param {T} target The changed type.
+   * @param {Transaction} transaction
+   */
+  constructor (target, transaction) {
+    /**
+     * The type on which this event was created on.
+     * @type {T}
+     */
+    this.target = target
+    /**
+     * The current target on which the observe callback is called.
+     * @type {AbstractType<any>}
+     */
+    this.currentTarget = target
+    /**
+     * The transaction that triggered this event.
+     * @type {Transaction}
+     */
+    this.transaction = transaction
+    /**
+     * @type {Object|null}
+     */
+    this._changes = null
+    /**
+     * @type {null | Map<string, { action: 'add' | 'update' | 'delete', oldValue: any, newValue: any }>}
+     */
+    this._keys = null
+    /**
+     * @type {null | Array<{ insert?: string | Array<any> | object | AbstractType<any>, retain?: number, delete?: number, attributes?: Object<string, any> }>}
+     */
+    this._delta = null
+    /**
+     * @type {Array<string|number>|null}
+     */
+    this._path = null
+  }
+
+  /**
+   * Computes the path from `y` to the changed type.
+   *
+   * @todo v14 should standardize on path: Array<{parent, index}> because that is easier to work with.
+   *
+   * The following property holds:
+   * @example
+   *   let type = y
+   *   event.path.forEach(dir => {
+   *     type = type.get(dir)
+   *   })
+   *   type === event.target // => true
+   */
+  get path () {
+    return this._path || (this._path = getPathTo(this.currentTarget, this.target))
+  }
+
+  /**
+   * Check if a struct is deleted by this event.
+   *
+   * In contrast to change.deleted, this method also returns true if the struct was added and then deleted.
+   *
+   * @param {AbstractStruct} struct
+   * @return {boolean}
+   */
+  deletes (struct) {
+    return isDeleted(this.transaction.deleteSet, struct.id)
+  }
+
+  /**
+   * @type {Map<string, { action: 'add' | 'update' | 'delete', oldValue: any, newValue: any }>}
+   */
+  get keys () {
+    if (this._keys === null) {
+      if (this.transaction.doc._transactionCleanups.length === 0) {
+        throw error.create(errorComputeChanges)
+      }
+      const keys = new Map()
+      const target = this.target
+      const changed = /** @type Set<string|null> */ (this.transaction.changed.get(target))
+      changed.forEach(key => {
+        if (key !== null) {
+          const item = /** @type {Item} */ (target._map.get(key))
+          /**
+           * @type {'delete' | 'add' | 'update'}
+           */
+          let action
+          let oldValue
+          if (this.adds(item)) {
+            let prev = item.left
+            while (prev !== null && this.adds(prev)) {
+              prev = prev.left
+            }
+            if (this.deletes(item)) {
+              if (prev !== null && this.deletes(prev)) {
+                action = 'delete'
+                oldValue = array.last(prev.content.getContent())
+              } else {
+                return
+              }
+            } else {
+              if (prev !== null && this.deletes(prev)) {
+                action = 'update'
+                oldValue = array.last(prev.content.getContent())
+              } else {
+                action = 'add'
+                oldValue = undefined
+              }
+            }
+          } else {
+            if (this.deletes(item)) {
+              action = 'delete'
+              oldValue = array.last(/** @type {Item} */ item.content.getContent())
+            } else {
+              return // nop
+            }
+          }
+          keys.set(key, { action, oldValue })
+        }
+      })
+      this._keys = keys
+    }
+    return this._keys
+  }
+
+  /**
+   * This is a computed property. Note that this can only be safely computed during the
+   * event call. Computing this property after other changes happened might result in
+   * unexpected behavior (incorrect computation of deltas). A safe way to collect changes
+   * is to store the `changes` or the `delta` object. Avoid storing the `transaction` object.
+   *
+   * @type {Array<{insert?: string | Array<any> | object | AbstractType<any>, retain?: number, delete?: number, attributes?: Object<string, any>}>}
+   */
+  get delta () {
+    return this.changes.delta
+  }
+
+  /**
+   * Check if a struct is added by this event.
+   *
+   * In contrast to change.deleted, this method also returns true if the struct was added and then deleted.
+   *
+   * @param {AbstractStruct} struct
+   * @return {boolean}
+   */
+  adds (struct) {
+    return struct.id.clock >= (this.transaction.beforeState.get(struct.id.client) || 0)
+  }
+
+  /**
+   * This is a computed property. Note that this can only be safely computed during the
+   * event call. Computing this property after other changes happened might result in
+   * unexpected behavior (incorrect computation of deltas). A safe way to collect changes
+   * is to store the `changes` or the `delta` object. Avoid storing the `transaction` object.
+   *
+   * @type {{added:Set<Item>,deleted:Set<Item>,keys:Map<string,{action:'add'|'update'|'delete',oldValue:any}>,delta:Array<{insert?:Array<any>|string, delete?:number, retain?:number}>}}
+   */
+  get changes () {
+    let changes = this._changes
+    if (changes === null) {
+      if (this.transaction.doc._transactionCleanups.length === 0) {
+        throw error.create(errorComputeChanges)
+      }
+      const target = this.target
+      const added = set.create()
+      const deleted = set.create()
+      /**
+       * @type {Array<{insert:Array<any>}|{delete:number}|{retain:number}>}
+       */
+      const delta = []
+      changes = {
+        added,
+        deleted,
+        delta,
+        keys: this.keys
+      }
+      const changed = /** @type Set<string|null> */ (this.transaction.changed.get(target))
+      if (changed.has(null)) {
+        /**
+         * @type {any}
+         */
+        let lastOp = null
+        const packOp = () => {
+          if (lastOp) {
+            delta.push(lastOp)
+          }
+        }
+        for (let item = target._start; item !== null; item = item.right) {
+          if (item.deleted) {
+            if (this.deletes(item) && !this.adds(item)) {
+              if (lastOp === null || lastOp.delete === undefined) {
+                packOp()
+                lastOp = { delete: 0 }
+              }
+              lastOp.delete += item.length
+              deleted.add(item)
+            } // else nop
+          } else {
+            if (this.adds(item)) {
+              if (lastOp === null || lastOp.insert === undefined) {
+                packOp()
+                lastOp = { insert: [] }
+              }
+              lastOp.insert = lastOp.insert.concat(item.content.getContent())
+              added.add(item)
+            } else {
+              if (lastOp === null || lastOp.retain === undefined) {
+                packOp()
+                lastOp = { retain: 0 }
+              }
+              lastOp.retain += item.length
+            }
+          }
+        }
+        if (lastOp !== null && lastOp.retain === undefined) {
+          packOp()
+        }
+      }
+      this._changes = changes
+    }
+    return /** @type {any} */ (changes)
+  }
+}
+
+/**
+ * Compute the path from this type to the specified target.
+ *
+ * @example
+ *   // `child` should be accessible via `type.get(path[0]).get(path[1])..`
+ *   const path = type.getPathTo(child)
+ *   // assuming `type instanceof YArray`
+ *   console.log(path) // might look like => [2, 'key1']
+ *   child === type.get(path[0]).get(path[1])
+ *
+ * @param {AbstractType<any>} parent
+ * @param {AbstractType<any>} child target
+ * @return {Array<string|number>} Path to the target
+ *
+ * @private
+ * @function
+ */
+const getPathTo = (parent, child) => {
+  const path = []
+  while (child._item !== null && child !== parent) {
+    if (child._item.parentSub !== null) {
+      // parent is map-ish
+      path.unshift(child._item.parentSub)
+    } else {
+      // parent is array-ish
+      let i = 0
+      let c = /** @type {AbstractType<any>} */ (child._item.parent)._start
+      while (c !== child._item && c !== null) {
+        if (!c.deleted && c.countable) {
+          i += c.length
+        }
+        c = c.right
+      }
+      path.unshift(i)
+    }
+    child = /** @type {AbstractType<any>} */ (child._item.parent)
+  }
+  return path
+}
--- a/src/utils/encoding.js
+++ b/src/utils/encoding.js
@ -0,0 +1,644 @@
+/**
+ * @module encoding
+ */
+/*
+ * We use the first five bits in the info flag for determining the type of the struct.
+ *
+ * 0: GC
+ * 1: Item with Deleted content
+ * 2: Item with JSON content
+ * 3: Item with Binary content
+ * 4: Item with String content
+ * 5: Item with Embed content (for richtext content)
+ * 6: Item with Format content (a formatting marker for richtext content)
+ * 7: Item with Type
+ */
+
+import {
+  findIndexSS,
+  getState,
+  createID,
+  getStateVector,
+  readAndApplyDeleteSet,
+  writeDeleteSet,
+  createDeleteSetFromStructStore,
+  transact,
+  readItemContent,
+  UpdateDecoderV1,
+  UpdateDecoderV2,
+  UpdateEncoderV1,
+  UpdateEncoderV2,
+  DSEncoderV2,
+  DSDecoderV1,
+  DSEncoderV1,
+  mergeUpdates,
+  mergeUpdatesV2,
+  Skip,
+  diffUpdateV2,
+  convertUpdateFormatV2ToV1,
+  DSDecoderV2, Doc, Transaction, GC, Item, StructStore // eslint-disable-line
+} from '../internals.js'
+
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as binary from 'lib0/binary'
+import * as map from 'lib0/map'
+import * as math from 'lib0/math'
+import * as array from 'lib0/array'
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Array<GC|Item>} structs All structs by `client`
+ * @param {number} client
+ * @param {number} clock write structs starting with `ID(client,clock)`
+ *
+ * @function
+ */
+const writeStructs = (encoder, structs, client, clock) => {
+  // write first id
+  clock = math.max(clock, structs[0].id.clock) // make sure the first id exists
+  const startNewStructs = findIndexSS(structs, clock)
+  // write # encoded structs
+  encoding.writeVarUint(encoder.restEncoder, structs.length - startNewStructs)
+  encoder.writeClient(client)
+  encoding.writeVarUint(encoder.restEncoder, clock)
+  const firstStruct = structs[startNewStructs]
+  // write first struct with an offset
+  firstStruct.write(encoder, clock - firstStruct.id.clock)
+  for (let i = startNewStructs + 1; i < structs.length; i++) {
+    structs[i].write(encoder, 0)
+  }
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {StructStore} store
+ * @param {Map<number,number>} _sm
+ *
+ * @private
+ * @function
+ */
+export const writeClientsStructs = (encoder, store, _sm) => {
+  // we filter all valid _sm entries into sm
+  const sm = new Map()
+  _sm.forEach((clock, client) => {
+    // only write if new structs are available
+    if (getState(store, client) > clock) {
+      sm.set(client, clock)
+    }
+  })
+  getStateVector(store).forEach((_clock, client) => {
+    if (!_sm.has(client)) {
+      sm.set(client, 0)
+    }
+  })
+  // write # states that were updated
+  encoding.writeVarUint(encoder.restEncoder, sm.size)
+  // Write items with higher client ids first
+  // This heavily improves the conflict algorithm.
+  array.from(sm.entries()).sort((a, b) => b[0] - a[0]).forEach(([client, clock]) => {
+    writeStructs(encoder, /** @type {Array<GC|Item>} */ (store.clients.get(client)), client, clock)
+  })
+}
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder The decoder object to read data from.
+ * @param {Doc} doc
+ * @return {Map<number, { i: number, refs: Array<Item | GC> }>}
+ *
+ * @private
+ * @function
+ */
+export const readClientsStructRefs = (decoder, doc) => {
+  /**
+   * @type {Map<number, { i: number, refs: Array<Item | GC> }>}
+   */
+  const clientRefs = map.create()
+  const numOfStateUpdates = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numOfStateUpdates; i++) {
+    const numberOfStructs = decoding.readVarUint(decoder.restDecoder)
+    /**
+     * @type {Array<GC|Item>}
+     */
+    const refs = new Array(numberOfStructs)
+    const client = decoder.readClient()
+    let clock = decoding.readVarUint(decoder.restDecoder)
+    // const start = performance.now()
+    clientRefs.set(client, { i: 0, refs })
+    for (let i = 0; i < numberOfStructs; i++) {
+      const info = decoder.readInfo()
+      switch (binary.BITS5 & info) {
+        case 0: { // GC
+          const len = decoder.readLen()
+          refs[i] = new GC(createID(client, clock), len)
+          clock += len
+          break
+        }
+        case 10: { // Skip Struct (nothing to apply)
+          // @todo we could reduce the amount of checks by adding Skip struct to clientRefs so we know that something is missing.
+          const len = decoding.readVarUint(decoder.restDecoder)
+          refs[i] = new Skip(createID(client, clock), len)
+          clock += len
+          break
+        }
+        default: { // Item with content
+          /**
+           * The optimized implementation doesn't use any variables because inlining variables is faster.
+           * Below a non-optimized version is shown that implements the basic algorithm with
+           * a few comments
+           */
+          const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+          // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+          // and we read the next string as parentYKey.
+          // It indicates how we store/retrieve parent from `y.share`
+          // @type {string|null}
+          const struct = new Item(
+            createID(client, clock),
+            null, // left
+            (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null, // origin
+            null, // right
+            (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null, // right origin
+            cantCopyParentInfo ? (decoder.readParentInfo() ? doc.get(decoder.readString()) : decoder.readLeftID()) : null, // parent
+            cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+            readItemContent(decoder, info) // item content
+          )
+          /* A non-optimized implementation of the above algorithm:
+
+          // The item that was originally to the left of this item.
+          const origin = (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null
+          // The item that was originally to the right of this item.
+          const rightOrigin = (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null
+          const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+          const hasParentYKey = cantCopyParentInfo ? decoder.readParentInfo() : false
+          // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+          // and we read the next string as parentYKey.
+          // It indicates how we store/retrieve parent from `y.share`
+          // @type {string|null}
+          const parentYKey = cantCopyParentInfo && hasParentYKey ? decoder.readString() : null
+
+          const struct = new Item(
+            createID(client, clock),
+            null, // left
+            origin, // origin
+            null, // right
+            rightOrigin, // right origin
+            cantCopyParentInfo && !hasParentYKey ? decoder.readLeftID() : (parentYKey !== null ? doc.get(parentYKey) : null), // parent
+            cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+            readItemContent(decoder, info) // item content
+          )
+          */
+          refs[i] = struct
+          clock += struct.length
+        }
+      }
+    }
+    // console.log('time to read: ', performance.now() - start) // @todo remove
+  }
+  return clientRefs
+}
+
+/**
+ * Resume computing structs generated by struct readers.
+ *
+ * While there is something to do, we integrate structs in this order
+ * 1. top element on stack, if stack is not empty
+ * 2. next element from current struct reader (if empty, use next struct reader)
+ *
+ * If struct causally depends on another struct (ref.missing), we put next reader of
+ * `ref.id.client` on top of stack.
+ *
+ * At some point we find a struct that has no causal dependencies,
+ * then we start emptying the stack.
+ *
+ * It is not possible to have circles: i.e. struct1 (from client1) depends on struct2 (from client2)
+ * depends on struct3 (from client1). Therefore the max stack size is equal to `structReaders.length`.
+ *
+ * This method is implemented in a way so that we can resume computation if this update
+ * causally depends on another update.
+ *
+ * @param {Transaction} transaction
+ * @param {StructStore} store
+ * @param {Map<number, { i: number, refs: (GC | Item)[] }>} clientsStructRefs
+ * @return { null | { update: Uint8Array, missing: Map<number,number> } }
+ *
+ * @private
+ * @function
+ */
+const integrateStructs = (transaction, store, clientsStructRefs) => {
+  /**
+   * @type {Array<Item | GC>}
+   */
+  const stack = []
+  // sort them so that we take the higher id first, in case of conflicts the lower id will probably not conflict with the id from the higher user.
+  let clientsStructRefsIds = array.from(clientsStructRefs.keys()).sort((a, b) => a - b)
+  if (clientsStructRefsIds.length === 0) {
+    return null
+  }
+  const getNextStructTarget = () => {
+    if (clientsStructRefsIds.length === 0) {
+      return null
+    }
+    let nextStructsTarget = /** @type {{i:number,refs:Array<GC|Item>}} */ (clientsStructRefs.get(clientsStructRefsIds[clientsStructRefsIds.length - 1]))
+    while (nextStructsTarget.refs.length === nextStructsTarget.i) {
+      clientsStructRefsIds.pop()
+      if (clientsStructRefsIds.length > 0) {
+        nextStructsTarget = /** @type {{i:number,refs:Array<GC|Item>}} */ (clientsStructRefs.get(clientsStructRefsIds[clientsStructRefsIds.length - 1]))
+      } else {
+        return null
+      }
+    }
+    return nextStructsTarget
+  }
+  let curStructsTarget = getNextStructTarget()
+  if (curStructsTarget === null) {
+    return null
+  }
+
+  /**
+   * @type {StructStore}
+   */
+  const restStructs = new StructStore()
+  const missingSV = new Map()
+  /**
+   * @param {number} client
+   * @param {number} clock
+   */
+  const updateMissingSv = (client, clock) => {
+    const mclock = missingSV.get(client)
+    if (mclock == null || mclock > clock) {
+      missingSV.set(client, clock)
+    }
+  }
+  /**
+   * @type {GC|Item}
+   */
+  let stackHead = /** @type {any} */ (curStructsTarget).refs[/** @type {any} */ (curStructsTarget).i++]
+  // caching the state because it is used very often
+  const state = new Map()
+
+  const addStackToRestSS = () => {
+    for (const item of stack) {
+      const client = item.id.client
+      const inapplicableItems = clientsStructRefs.get(client)
+      if (inapplicableItems) {
+        // decrement because we weren't able to apply previous operation
+        inapplicableItems.i--
+        restStructs.clients.set(client, inapplicableItems.refs.slice(inapplicableItems.i))
+        clientsStructRefs.delete(client)
+        inapplicableItems.i = 0
+        inapplicableItems.refs = []
+      } else {
+        // item was the last item on clientsStructRefs and the field was already cleared. Add item to restStructs and continue
+        restStructs.clients.set(client, [item])
+      }
+      // remove client from clientsStructRefsIds to prevent users from applying the same update again
+      clientsStructRefsIds = clientsStructRefsIds.filter(c => c !== client)
+    }
+    stack.length = 0
+  }
+
+  // iterate over all struct readers until we are done
+  while (true) {
+    if (stackHead.constructor !== Skip) {
+      const localClock = map.setIfUndefined(state, stackHead.id.client, () => getState(store, stackHead.id.client))
+      const offset = localClock - stackHead.id.clock
+      if (offset < 0) {
+        // update from the same client is missing
+        stack.push(stackHead)
+        updateMissingSv(stackHead.id.client, stackHead.id.clock - 1)
+        // hid a dead wall, add all items from stack to restSS
+        addStackToRestSS()
+      } else {
+        const missing = stackHead.getMissing(transaction, store)
+        if (missing !== null) {
+          stack.push(stackHead)
+          // get the struct reader that has the missing struct
+          /**
+           * @type {{ refs: Array<GC|Item>, i: number }}
+           */
+          const structRefs = clientsStructRefs.get(/** @type {number} */ (missing)) || { refs: [], i: 0 }
+          if (structRefs.refs.length === structRefs.i) {
+            // This update message causally depends on another update message that doesn't exist yet
+            updateMissingSv(/** @type {number} */ (missing), getState(store, missing))
+            addStackToRestSS()
+          } else {
+            stackHead = structRefs.refs[structRefs.i++]
+            continue
+          }
+        } else if (offset === 0 || offset < stackHead.length) {
+          // all fine, apply the stackhead
+          stackHead.integrate(transaction, offset)
+          state.set(stackHead.id.client, stackHead.id.clock + stackHead.length)
+        }
+      }
+    }
+    // iterate to next stackHead
+    if (stack.length > 0) {
+      stackHead = /** @type {GC|Item} */ (stack.pop())
+    } else if (curStructsTarget !== null && curStructsTarget.i < curStructsTarget.refs.length) {
+      stackHead = /** @type {GC|Item} */ (curStructsTarget.refs[curStructsTarget.i++])
+    } else {
+      curStructsTarget = getNextStructTarget()
+      if (curStructsTarget === null) {
+        // we are done!
+        break
+      } else {
+        stackHead = /** @type {GC|Item} */ (curStructsTarget.refs[curStructsTarget.i++])
+      }
+    }
+  }
+  if (restStructs.clients.size > 0) {
+    const encoder = new UpdateEncoderV2()
+    writeClientsStructs(encoder, restStructs, new Map())
+    // write empty deleteset
+    // writeDeleteSet(encoder, new DeleteSet())
+    encoding.writeVarUint(encoder.restEncoder, 0) // => no need for an extra function call, just write 0 deletes
+    return { missing: missingSV, update: encoder.toUint8Array() }
+  }
+  return null
+}
+
+/**
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Transaction} transaction
+ *
+ * @private
+ * @function
+ */
+export const writeStructsFromTransaction = (encoder, transaction) => writeClientsStructs(encoder, transaction.doc.store, transaction.beforeState)
+
+/**
+ * Read and apply a document update.
+ *
+ * This function has the same effect as `applyUpdate` but accepts a decoder.
+ *
+ * @param {decoding.Decoder} decoder
+ * @param {Doc} ydoc
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} [structDecoder]
+ *
+ * @function
+ */
+export const readUpdateV2 = (decoder, ydoc, transactionOrigin, structDecoder = new UpdateDecoderV2(decoder)) =>
+  transact(ydoc, transaction => {
+    // force that transaction.local is set to non-local
+    transaction.local = false
+    let retry = false
+    const doc = transaction.doc
+    const store = doc.store
+    // let start = performance.now()
+    const ss = readClientsStructRefs(structDecoder, doc)
+    // console.log('time to read structs: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    // console.log('time to merge: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    const restStructs = integrateStructs(transaction, store, ss)
+    const pending = store.pendingStructs
+    if (pending) {
+      // check if we can apply something
+      for (const [client, clock] of pending.missing) {
+        if (clock < getState(store, client)) {
+          retry = true
+          break
+        }
+      }
+      if (restStructs) {
+        // merge restStructs into store.pending
+        for (const [client, clock] of restStructs.missing) {
+          const mclock = pending.missing.get(client)
+          if (mclock == null || mclock > clock) {
+            pending.missing.set(client, clock)
+          }
+        }
+        pending.update = mergeUpdatesV2([pending.update, restStructs.update])
+      }
+    } else {
+      store.pendingStructs = restStructs
+    }
+    // console.log('time to integrate: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    const dsRest = readAndApplyDeleteSet(structDecoder, transaction, store)
+    if (store.pendingDs) {
+      // @todo we could make a lower-bound state-vector check as we do above
+      const pendingDSUpdate = new UpdateDecoderV2(decoding.createDecoder(store.pendingDs))
+      decoding.readVarUint(pendingDSUpdate.restDecoder) // read 0 structs, because we only encode deletes in pendingdsupdate
+      const dsRest2 = readAndApplyDeleteSet(pendingDSUpdate, transaction, store)
+      if (dsRest && dsRest2) {
+        // case 1: ds1 != null && ds2 != null
+        store.pendingDs = mergeUpdatesV2([dsRest, dsRest2])
+      } else {
+        // case 2: ds1 != null
+        // case 3: ds2 != null
+        // case 4: ds1 == null && ds2 == null
+        store.pendingDs = dsRest || dsRest2
+      }
+    } else {
+      // Either dsRest == null && pendingDs == null OR dsRest != null
+      store.pendingDs = dsRest
+    }
+    // console.log('time to cleanup: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+
+    // console.log('time to resume delete readers: ', performance.now() - start) // @todo remove
+    // start = performance.now()
+    if (retry) {
+      const update = /** @type {{update: Uint8Array}} */ (store.pendingStructs).update
+      store.pendingStructs = null
+      applyUpdateV2(transaction.doc, update)
+    }
+  }, transactionOrigin, false)
+
+/**
+ * Read and apply a document update.
+ *
+ * This function has the same effect as `applyUpdate` but accepts a decoder.
+ *
+ * @param {decoding.Decoder} decoder
+ * @param {Doc} ydoc
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ *
+ * @function
+ */
+export const readUpdate = (decoder, ydoc, transactionOrigin) => readUpdateV2(decoder, ydoc, transactionOrigin, new UpdateDecoderV1(decoder))
+
+/**
+ * Apply a document update created by, for example, `y.on('update', update => ..)` or `update = encodeStateAsUpdate()`.
+ *
+ * This function has the same effect as `readUpdate` but accepts an Uint8Array instead of a Decoder.
+ *
+ * @param {Doc} ydoc
+ * @param {Uint8Array} update
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ *
+ * @function
+ */
+export const applyUpdateV2 = (ydoc, update, transactionOrigin, YDecoder = UpdateDecoderV2) => {
+  const decoder = decoding.createDecoder(update)
+  readUpdateV2(decoder, ydoc, transactionOrigin, new YDecoder(decoder))
+}
+
+/**
+ * Apply a document update created by, for example, `y.on('update', update => ..)` or `update = encodeStateAsUpdate()`.
+ *
+ * This function has the same effect as `readUpdate` but accepts an Uint8Array instead of a Decoder.
+ *
+ * @param {Doc} ydoc
+ * @param {Uint8Array} update
+ * @param {any} [transactionOrigin] This will be stored on `transaction.origin` and `.on('update', (update, origin))`
+ *
+ * @function
+ */
+export const applyUpdate = (ydoc, update, transactionOrigin) => applyUpdateV2(ydoc, update, transactionOrigin, UpdateDecoderV1)
+
+/**
+ * Write all the document as a single update message. If you specify the state of the remote client (`targetStateVector`) it will
+ * only write the operations that are missing.
+ *
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+ * @param {Doc} doc
+ * @param {Map<number,number>} [targetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ *
+ * @function
+ */
+export const writeStateAsUpdate = (encoder, doc, targetStateVector = new Map()) => {
+  writeClientsStructs(encoder, doc.store, targetStateVector)
+  writeDeleteSet(encoder, createDeleteSetFromStructStore(doc.store))
+}
+
+/**
+ * Write all the document as a single update message that can be applied on the remote document. If you specify the state of the remote client (`targetState`) it will
+ * only write the operations that are missing.
+ *
+ * Use `writeStateAsUpdate` instead if you are working with lib0/encoding.js#Encoder
+ *
+ * @param {Doc} doc
+ * @param {Uint8Array} [encodedTargetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ * @param {UpdateEncoderV1 | UpdateEncoderV2} [encoder]
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateAsUpdateV2 = (doc, encodedTargetStateVector = new Uint8Array([0]), encoder = new UpdateEncoderV2()) => {
+  const targetStateVector = decodeStateVector(encodedTargetStateVector)
+  writeStateAsUpdate(encoder, doc, targetStateVector)
+  const updates = [encoder.toUint8Array()]
+  // also add the pending updates (if there are any)
+  if (doc.store.pendingDs) {
+    updates.push(doc.store.pendingDs)
+  }
+  if (doc.store.pendingStructs) {
+    updates.push(diffUpdateV2(doc.store.pendingStructs.update, encodedTargetStateVector))
+  }
+  if (updates.length > 1) {
+    if (encoder.constructor === UpdateEncoderV1) {
+      return mergeUpdates(updates.map((update, i) => i === 0 ? update : convertUpdateFormatV2ToV1(update)))
+    } else if (encoder.constructor === UpdateEncoderV2) {
+      return mergeUpdatesV2(updates)
+    }
+  }
+  return updates[0]
+}
+
+/**
+ * Write all the document as a single update message that can be applied on the remote document. If you specify the state of the remote client (`targetState`) it will
+ * only write the operations that are missing.
+ *
+ * Use `writeStateAsUpdate` instead if you are working with lib0/encoding.js#Encoder
+ *
+ * @param {Doc} doc
+ * @param {Uint8Array} [encodedTargetStateVector] The state of the target that receives the update. Leave empty to write all known structs
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateAsUpdate = (doc, encodedTargetStateVector) => encodeStateAsUpdateV2(doc, encodedTargetStateVector, new UpdateEncoderV1())
+
+/**
+ * Read state vector from Decoder and return as Map
+ *
+ * @param {DSDecoderV1 | DSDecoderV2} decoder
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+export const readStateVector = decoder => {
+  const ss = new Map()
+  const ssLength = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < ssLength; i++) {
+    const client = decoding.readVarUint(decoder.restDecoder)
+    const clock = decoding.readVarUint(decoder.restDecoder)
+    ss.set(client, clock)
+  }
+  return ss
+}
+
+/**
+ * Read decodedState and return State as Map.
+ *
+ * @param {Uint8Array} decodedState
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+// export const decodeStateVectorV2 = decodedState => readStateVector(new DSDecoderV2(decoding.createDecoder(decodedState)))
+
+/**
+ * Read decodedState and return State as Map.
+ *
+ * @param {Uint8Array} decodedState
+ * @return {Map<number,number>} Maps `client` to the number next expected `clock` from that client.
+ *
+ * @function
+ */
+export const decodeStateVector = decodedState => readStateVector(new DSDecoderV1(decoding.createDecoder(decodedState)))
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {Map<number,number>} sv
+ * @function
+ */
+export const writeStateVector = (encoder, sv) => {
+  encoding.writeVarUint(encoder.restEncoder, sv.size)
+  array.from(sv.entries()).sort((a, b) => b[0] - a[0]).forEach(([client, clock]) => {
+    encoding.writeVarUint(encoder.restEncoder, client) // @todo use a special client decoder that is based on mapping
+    encoding.writeVarUint(encoder.restEncoder, clock)
+  })
+  return encoder
+}
+
+/**
+ * @param {DSEncoderV1 | DSEncoderV2} encoder
+ * @param {Doc} doc
+ *
+ * @function
+ */
+export const writeDocumentStateVector = (encoder, doc) => writeStateVector(encoder, getStateVector(doc.store))
+
+/**
+ * Encode State as Uint8Array.
+ *
+ * @param {Doc|Map<number,number>} doc
+ * @param {DSEncoderV1 | DSEncoderV2} [encoder]
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateVectorV2 = (doc, encoder = new DSEncoderV2()) => {
+  if (doc instanceof Map) {
+    writeStateVector(encoder, doc)
+  } else {
+    writeDocumentStateVector(encoder, doc)
+  }
+  return encoder.toUint8Array()
+}
+
+/**
+ * Encode State as Uint8Array.
+ *
+ * @param {Doc|Map<number,number>} doc
+ * @return {Uint8Array}
+ *
+ * @function
+ */
+export const encodeStateVector = doc => encodeStateVectorV2(doc, new DSEncoderV1())
--- a/src/utils/isParentOf.js
+++ b/src/utils/isParentOf.js
@ -0,0 +1,21 @@
+import { AbstractType, Item } from '../internals.js' // eslint-disable-line
+
+/**
+ * Check if `parent` is a parent of `child`.
+ *
+ * @param {AbstractType<any>} parent
+ * @param {Item|null} child
+ * @return {Boolean} Whether `parent` is a parent of `child`.
+ *
+ * @private
+ * @function
+ */
+export const isParentOf = (parent, child) => {
+  while (child !== null) {
+    if (child.parent === parent) {
+      return true
+    }
+    child = /** @type {AbstractType<any>} */ (child.parent)._item
+  }
+  return false
+}
--- a/src/utils/logging.js
+++ b/src/utils/logging.js
@ -0,0 +1,21 @@
+import {
+  AbstractType // eslint-disable-line
+} from '../internals.js'
+
+/**
+ * Convenient helper to log type information.
+ *
+ * Do not use in productive systems as the output can be immense!
+ *
+ * @param {AbstractType<any>} type
+ */
+export const logType = type => {
+  const res = []
+  let n = type._start
+  while (n) {
+    res.push(n)
+    n = n.right
+  }
+  console.log('Children: ', res)
+  console.log('Children content: ', res.filter(m => !m.deleted).map(m => m.content))
+}
--- a/src/utils/updates.js
+++ b/src/utils/updates.js
@ -0,0 +1,722 @@
+import * as binary from 'lib0/binary'
+import * as decoding from 'lib0/decoding'
+import * as encoding from 'lib0/encoding'
+import * as error from 'lib0/error'
+import * as f from 'lib0/function'
+import * as logging from 'lib0/logging'
+import * as map from 'lib0/map'
+import * as math from 'lib0/math'
+import * as string from 'lib0/string'
+
+import {
+  ContentAny,
+  ContentBinary,
+  ContentDeleted,
+  ContentDoc,
+  ContentEmbed,
+  ContentFormat,
+  ContentJSON,
+  ContentString,
+  ContentType,
+  createID,
+  decodeStateVector,
+  DSEncoderV1,
+  DSEncoderV2,
+  GC,
+  Item,
+  mergeDeleteSets,
+  readDeleteSet,
+  readItemContent,
+  Skip,
+  UpdateDecoderV1,
+  UpdateDecoderV2,
+  UpdateEncoderV1,
+  UpdateEncoderV2,
+  writeDeleteSet,
+  YXmlElement,
+  YXmlHook
+} from '../internals.js'
+
+/**
+ * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+ */
+function * lazyStructReaderGenerator (decoder) {
+  const numOfStateUpdates = decoding.readVarUint(decoder.restDecoder)
+  for (let i = 0; i < numOfStateUpdates; i++) {
+    const numberOfStructs = decoding.readVarUint(decoder.restDecoder)
+    const client = decoder.readClient()
+    let clock = decoding.readVarUint(decoder.restDecoder)
+    for (let i = 0; i < numberOfStructs; i++) {
+      const info = decoder.readInfo()
+      // @todo use switch instead of ifs
+      if (info === 10) {
+        const len = decoding.readVarUint(decoder.restDecoder)
+        yield new Skip(createID(client, clock), len)
+        clock += len
+      } else if ((binary.BITS5 & info) !== 0) {
+        const cantCopyParentInfo = (info & (binary.BIT7 | binary.BIT8)) === 0
+        // If parent = null and neither left nor right are defined, then we know that `parent` is child of `y`
+        // and we read the next string as parentYKey.
+        // It indicates how we store/retrieve parent from `y.share`
+        // @type {string|null}
+        const struct = new Item(
+          createID(client, clock),
+          null, // left
+          (info & binary.BIT8) === binary.BIT8 ? decoder.readLeftID() : null, // origin
+          null, // right
+          (info & binary.BIT7) === binary.BIT7 ? decoder.readRightID() : null, // right origin
+          // @ts-ignore Force writing a string here.
+          cantCopyParentInfo ? (decoder.readParentInfo() ? decoder.readString() : decoder.readLeftID()) : null, // parent
+          cantCopyParentInfo && (info & binary.BIT6) === binary.BIT6 ? decoder.readString() : null, // parentSub
+          readItemContent(decoder, info) // item content
+        )
+        yield struct
+        clock += struct.length
+      } else {
+        const len = decoder.readLen()
+        yield new GC(createID(client, clock), len)
+        clock += len
+      }
+    }
+  }
+}
+
+export class LazyStructReader {
+  /**
+   * @param {UpdateDecoderV1 | UpdateDecoderV2} decoder
+   * @param {boolean} filterSkips
+   */
+  constructor (decoder, filterSkips) {
+    this.gen = lazyStructReaderGenerator(decoder)
+    /**
+     * @type {null | Item | Skip | GC}
+     */
+    this.curr = null
+    this.done = false
+    this.filterSkips = filterSkips
+    this.next()
+  }
+
+  /**
+   * @return {Item | GC | Skip |null}
+   */
+  next () {
+    // ignore "Skip" structs
+    do {
+      this.curr = this.gen.next().value || null
+    } while (this.filterSkips && this.curr !== null && this.curr.constructor === Skip)
+    return this.curr
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ *
+ */
+export const logUpdate = update => logUpdateV2(update, UpdateDecoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} [YDecoder]
+ *
+ */
+export const logUpdateV2 = (update, YDecoder = UpdateDecoderV2) => {
+  const structs = []
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    structs.push(curr)
+  }
+  logging.print('Structs: ', structs)
+  const ds = readDeleteSet(updateDecoder)
+  logging.print('DeleteSet: ', ds)
+}
+
+/**
+ * @param {Uint8Array} update
+ *
+ */
+export const decodeUpdate = (update) => decodeUpdateV2(update, UpdateDecoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} [YDecoder]
+ *
+ */
+export const decodeUpdateV2 = (update, YDecoder = UpdateDecoderV2) => {
+  const structs = []
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    structs.push(curr)
+  }
+  return {
+    structs,
+    ds: readDeleteSet(updateDecoder)
+  }
+}
+
+export class LazyStructWriter {
+  /**
+   * @param {UpdateEncoderV1 | UpdateEncoderV2} encoder
+   */
+  constructor (encoder) {
+    this.currClient = 0
+    this.startClock = 0
+    this.written = 0
+    this.encoder = encoder
+    /**
+     * We want to write operations lazily, but also we need to know beforehand how many operations we want to write for each client.
+     *
+     * This kind of meta-information (#clients, #structs-per-client-written) is written to the restEncoder.
+     *
+     * We fragment the restEncoder and store a slice of it per-client until we know how many clients there are.
+     * When we flush (toUint8Array) we write the restEncoder using the fragments and the meta-information.
+     *
+     * @type {Array<{ written: number, restEncoder: Uint8Array }>}
+     */
+    this.clientStructs = []
+  }
+}
+
+/**
+ * @param {Array<Uint8Array>} updates
+ * @return {Uint8Array}
+ */
+export const mergeUpdates = updates => mergeUpdatesV2(updates, UpdateDecoderV1, UpdateEncoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof DSEncoderV1 | typeof DSEncoderV2} YEncoder
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} YDecoder
+ * @return {Uint8Array}
+ */
+export const encodeStateVectorFromUpdateV2 = (update, YEncoder = DSEncoderV2, YDecoder = UpdateDecoderV2) => {
+  const encoder = new YEncoder()
+  const updateDecoder = new LazyStructReader(new YDecoder(decoding.createDecoder(update)), false)
+  let curr = updateDecoder.curr
+  if (curr !== null) {
+    let size = 0
+    let currClient = curr.id.client
+    let stopCounting = curr.id.clock !== 0 // must start at 0
+    let currClock = stopCounting ? 0 : curr.id.clock + curr.length
+    for (; curr !== null; curr = updateDecoder.next()) {
+      if (currClient !== curr.id.client) {
+        if (currClock !== 0) {
+          size++
+          // We found a new client
+          // write what we have to the encoder
+          encoding.writeVarUint(encoder.restEncoder, currClient)
+          encoding.writeVarUint(encoder.restEncoder, currClock)
+        }
+        currClient = curr.id.client
+        currClock = 0
+        stopCounting = curr.id.clock !== 0
+      }
+      // we ignore skips
+      if (curr.constructor === Skip) {
+        stopCounting = true
+      }
+      if (!stopCounting) {
+        currClock = curr.id.clock + curr.length
+      }
+    }
+    // write what we have
+    if (currClock !== 0) {
+      size++
+      encoding.writeVarUint(encoder.restEncoder, currClient)
+      encoding.writeVarUint(encoder.restEncoder, currClock)
+    }
+    // prepend the size of the state vector
+    const enc = encoding.createEncoder()
+    encoding.writeVarUint(enc, size)
+    encoding.writeBinaryEncoder(enc, encoder.restEncoder)
+    encoder.restEncoder = enc
+    return encoder.toUint8Array()
+  } else {
+    encoding.writeVarUint(encoder.restEncoder, 0)
+    return encoder.toUint8Array()
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @return {Uint8Array}
+ */
+export const encodeStateVectorFromUpdate = update => encodeStateVectorFromUpdateV2(update, DSEncoderV1, UpdateDecoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} YDecoder
+ * @return {{ from: Map<number,number>, to: Map<number,number> }}
+ */
+export const parseUpdateMetaV2 = (update, YDecoder = UpdateDecoderV2) => {
+  /**
+   * @type {Map<number, number>}
+   */
+  const from = new Map()
+  /**
+   * @type {Map<number, number>}
+   */
+  const to = new Map()
+  const updateDecoder = new LazyStructReader(new YDecoder(decoding.createDecoder(update)), false)
+  let curr = updateDecoder.curr
+  if (curr !== null) {
+    let currClient = curr.id.client
+    let currClock = curr.id.clock
+    // write the beginning to `from`
+    from.set(currClient, currClock)
+    for (; curr !== null; curr = updateDecoder.next()) {
+      if (currClient !== curr.id.client) {
+        // We found a new client
+        // write the end to `to`
+        to.set(currClient, currClock)
+        // write the beginning to `from`
+        from.set(curr.id.client, curr.id.clock)
+        // update currClient
+        currClient = curr.id.client
+      }
+      currClock = curr.id.clock + curr.length
+    }
+    // write the end to `to`
+    to.set(currClient, currClock)
+  }
+  return { from, to }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @return {{ from: Map<number,number>, to: Map<number,number> }}
+ */
+export const parseUpdateMeta = update => parseUpdateMetaV2(update, UpdateDecoderV1)
+
+/**
+ * This method is intended to slice any kind of struct and retrieve the right part.
+ * It does not handle side-effects, so it should only be used by the lazy-encoder.
+ *
+ * @param {Item | GC | Skip} left
+ * @param {number} diff
+ * @return {Item | GC}
+ */
+const sliceStruct = (left, diff) => {
+  if (left.constructor === GC) {
+    const { client, clock } = left.id
+    return new GC(createID(client, clock + diff), left.length - diff)
+  } else if (left.constructor === Skip) {
+    const { client, clock } = left.id
+    return new Skip(createID(client, clock + diff), left.length - diff)
+  } else {
+    const leftItem = /** @type {Item} */ (left)
+    const { client, clock } = leftItem.id
+    return new Item(
+      createID(client, clock + diff),
+      null,
+      createID(client, clock + diff - 1),
+      null,
+      leftItem.rightOrigin,
+      leftItem.parent,
+      leftItem.parentSub,
+      leftItem.content.splice(diff)
+    )
+  }
+}
+
+/**
+ *
+ * This function works similarly to `readUpdateV2`.
+ *
+ * @param {Array<Uint8Array>} updates
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ * @param {typeof UpdateEncoderV1 | typeof UpdateEncoderV2} [YEncoder]
+ * @return {Uint8Array}
+ */
+export const mergeUpdatesV2 = (updates, YDecoder = UpdateDecoderV2, YEncoder = UpdateEncoderV2) => {
+  if (updates.length === 1) {
+    return updates[0]
+  }
+  const updateDecoders = updates.map(update => new YDecoder(decoding.createDecoder(update)))
+  let lazyStructDecoders = updateDecoders.map(decoder => new LazyStructReader(decoder, true))
+
+  /**
+   * @todo we don't need offset because we always slice before
+   * @type {null | { struct: Item | GC | Skip, offset: number }}
+   */
+  let currWrite = null
+
+  const updateEncoder = new YEncoder()
+  // write structs lazily
+  const lazyStructEncoder = new LazyStructWriter(updateEncoder)
+
+  // Note: We need to ensure that all lazyStructDecoders are fully consumed
+  // Note: Should merge document updates whenever possible - even from different updates
+  // Note: Should handle that some operations cannot be applied yet ()
+
+  while (true) {
+    // Write higher clients first ⇒ sort by clientID & clock and remove decoders without content
+    lazyStructDecoders = lazyStructDecoders.filter(dec => dec.curr !== null)
+    lazyStructDecoders.sort(
+      /** @type {function(any,any):number} */ (dec1, dec2) => {
+        if (dec1.curr.id.client === dec2.curr.id.client) {
+          const clockDiff = dec1.curr.id.clock - dec2.curr.id.clock
+          if (clockDiff === 0) {
+            // @todo remove references to skip since the structDecoders must filter Skips.
+            return dec1.curr.constructor === dec2.curr.constructor
+              ? 0
+              : dec1.curr.constructor === Skip ? 1 : -1 // we are filtering skips anyway.
+          } else {
+            return clockDiff
+          }
+        } else {
+          return dec2.curr.id.client - dec1.curr.id.client
+        }
+      }
+    )
+    if (lazyStructDecoders.length === 0) {
+      break
+    }
+    const currDecoder = lazyStructDecoders[0]
+    // write from currDecoder until the next operation is from another client or if filler-struct
+    // then we need to reorder the decoders and find the next operation to write
+    const firstClient = /** @type {Item | GC} */ (currDecoder.curr).id.client
+
+    if (currWrite !== null) {
+      let curr = /** @type {Item | GC | null} */ (currDecoder.curr)
+      let iterated = false
+
+      // iterate until we find something that we haven't written already
+      // remember: first the high client-ids are written
+      while (curr !== null && curr.id.clock + curr.length <= currWrite.struct.id.clock + currWrite.struct.length && curr.id.client >= currWrite.struct.id.client) {
+        curr = currDecoder.next()
+        iterated = true
+      }
+      if (
+        curr === null || // current decoder is empty
+        curr.id.client !== firstClient || // check whether there is another decoder that has has updates from `firstClient`
+        (iterated && curr.id.clock > currWrite.struct.id.clock + currWrite.struct.length) // the above while loop was used and we are potentially missing updates
+      ) {
+        continue
+      }
+
+      if (firstClient !== currWrite.struct.id.client) {
+        writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+        currWrite = { struct: curr, offset: 0 }
+        currDecoder.next()
+      } else {
+        if (currWrite.struct.id.clock + currWrite.struct.length < curr.id.clock) {
+          // @todo write currStruct & set currStruct = Skip(clock = currStruct.id.clock + currStruct.length, length = curr.id.clock - self.clock)
+          if (currWrite.struct.constructor === Skip) {
+            // extend existing skip
+            currWrite.struct.length = curr.id.clock + curr.length - currWrite.struct.id.clock
+          } else {
+            writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+            const diff = curr.id.clock - currWrite.struct.id.clock - currWrite.struct.length
+            /**
+             * @type {Skip}
+             */
+            const struct = new Skip(createID(firstClient, currWrite.struct.id.clock + currWrite.struct.length), diff)
+            currWrite = { struct, offset: 0 }
+          }
+        } else { // if (currWrite.struct.id.clock + currWrite.struct.length >= curr.id.clock) {
+          const diff = currWrite.struct.id.clock + currWrite.struct.length - curr.id.clock
+          if (diff > 0) {
+            if (currWrite.struct.constructor === Skip) {
+              // prefer to slice Skip because the other struct might contain more information
+              currWrite.struct.length -= diff
+            } else {
+              curr = sliceStruct(curr, diff)
+            }
+          }
+          if (!currWrite.struct.mergeWith(/** @type {any} */ (curr))) {
+            writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+            currWrite = { struct: curr, offset: 0 }
+            currDecoder.next()
+          }
+        }
+      }
+    } else {
+      currWrite = { struct: /** @type {Item | GC} */ (currDecoder.curr), offset: 0 }
+      currDecoder.next()
+    }
+    for (
+      let next = currDecoder.curr;
+      next !== null && next.id.client === firstClient && next.id.clock === currWrite.struct.id.clock + currWrite.struct.length && next.constructor !== Skip;
+      next = currDecoder.next()
+    ) {
+      writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+      currWrite = { struct: next, offset: 0 }
+    }
+  }
+  if (currWrite !== null) {
+    writeStructToLazyStructWriter(lazyStructEncoder, currWrite.struct, currWrite.offset)
+    currWrite = null
+  }
+  finishLazyStructWriting(lazyStructEncoder)
+
+  const dss = updateDecoders.map(decoder => readDeleteSet(decoder))
+  const ds = mergeDeleteSets(dss)
+  writeDeleteSet(updateEncoder, ds)
+  return updateEncoder.toUint8Array()
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {Uint8Array} sv
+ * @param {typeof UpdateDecoderV1 | typeof UpdateDecoderV2} [YDecoder]
+ * @param {typeof UpdateEncoderV1 | typeof UpdateEncoderV2} [YEncoder]
+ */
+export const diffUpdateV2 = (update, sv, YDecoder = UpdateDecoderV2, YEncoder = UpdateEncoderV2) => {
+  const state = decodeStateVector(sv)
+  const encoder = new YEncoder()
+  const lazyStructWriter = new LazyStructWriter(encoder)
+  const decoder = new YDecoder(decoding.createDecoder(update))
+  const reader = new LazyStructReader(decoder, false)
+  while (reader.curr) {
+    const curr = reader.curr
+    const currClient = curr.id.client
+    const svClock = state.get(currClient) || 0
+    if (reader.curr.constructor === Skip) {
+      // the first written struct shouldn't be a skip
+      reader.next()
+      continue
+    }
+    if (curr.id.clock + curr.length > svClock) {
+      writeStructToLazyStructWriter(lazyStructWriter, curr, math.max(svClock - curr.id.clock, 0))
+      reader.next()
+      while (reader.curr && reader.curr.id.client === currClient) {
+        writeStructToLazyStructWriter(lazyStructWriter, reader.curr, 0)
+        reader.next()
+      }
+    } else {
+      // read until something new comes up
+      while (reader.curr && reader.curr.id.client === currClient && reader.curr.id.clock + reader.curr.length <= svClock) {
+        reader.next()
+      }
+    }
+  }
+  finishLazyStructWriting(lazyStructWriter)
+  // write ds
+  const ds = readDeleteSet(decoder)
+  writeDeleteSet(encoder, ds)
+  return encoder.toUint8Array()
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {Uint8Array} sv
+ */
+export const diffUpdate = (update, sv) => diffUpdateV2(update, sv, UpdateDecoderV1, UpdateEncoderV1)
+
+/**
+ * @param {LazyStructWriter} lazyWriter
+ */
+const flushLazyStructWriter = lazyWriter => {
+  if (lazyWriter.written > 0) {
+    lazyWriter.clientStructs.push({ written: lazyWriter.written, restEncoder: encoding.toUint8Array(lazyWriter.encoder.restEncoder) })
+    lazyWriter.encoder.restEncoder = encoding.createEncoder()
+    lazyWriter.written = 0
+  }
+}
+
+/**
+ * @param {LazyStructWriter} lazyWriter
+ * @param {Item | GC} struct
+ * @param {number} offset
+ */
+const writeStructToLazyStructWriter = (lazyWriter, struct, offset) => {
+  // flush curr if we start another client
+  if (lazyWriter.written > 0 && lazyWriter.currClient !== struct.id.client) {
+    flushLazyStructWriter(lazyWriter)
+  }
+  if (lazyWriter.written === 0) {
+    lazyWriter.currClient = struct.id.client
+    // write next client
+    lazyWriter.encoder.writeClient(struct.id.client)
+    // write startClock
+    encoding.writeVarUint(lazyWriter.encoder.restEncoder, struct.id.clock + offset)
+  }
+  struct.write(lazyWriter.encoder, offset)
+  lazyWriter.written++
+}
+/**
+ * Call this function when we collected all parts and want to
+ * put all the parts together. After calling this method,
+ * you can continue using the UpdateEncoder.
+ *
+ * @param {LazyStructWriter} lazyWriter
+ */
+const finishLazyStructWriting = (lazyWriter) => {
+  flushLazyStructWriter(lazyWriter)
+
+  // this is a fresh encoder because we called flushCurr
+  const restEncoder = lazyWriter.encoder.restEncoder
+
+  /**
+   * Now we put all the fragments together.
+   * This works similarly to `writeClientsStructs`
+   */
+
+  // write # states that were updated - i.e. the clients
+  encoding.writeVarUint(restEncoder, lazyWriter.clientStructs.length)
+
+  for (let i = 0; i < lazyWriter.clientStructs.length; i++) {
+    const partStructs = lazyWriter.clientStructs[i]
+    /**
+     * Works similarly to `writeStructs`
+     */
+    // write # encoded structs
+    encoding.writeVarUint(restEncoder, partStructs.written)
+    // write the rest of the fragment
+    encoding.writeUint8Array(restEncoder, partStructs.restEncoder)
+  }
+}
+
+/**
+ * @param {Uint8Array} update
+ * @param {function(Item|GC|Skip):Item|GC|Skip} blockTransformer
+ * @param {typeof UpdateDecoderV2 | typeof UpdateDecoderV1} YDecoder
+ * @param {typeof UpdateEncoderV2 | typeof UpdateEncoderV1 } YEncoder
+ */
+export const convertUpdateFormat = (update, blockTransformer, YDecoder, YEncoder) => {
+  const updateDecoder = new YDecoder(decoding.createDecoder(update))
+  const lazyDecoder = new LazyStructReader(updateDecoder, false)
+  const updateEncoder = new YEncoder()
+  const lazyWriter = new LazyStructWriter(updateEncoder)
+  for (let curr = lazyDecoder.curr; curr !== null; curr = lazyDecoder.next()) {
+    writeStructToLazyStructWriter(lazyWriter, blockTransformer(curr), 0)
+  }
+  finishLazyStructWriting(lazyWriter)
+  const ds = readDeleteSet(updateDecoder)
+  writeDeleteSet(updateEncoder, ds)
+  return updateEncoder.toUint8Array()
+}
+
+/**
+ * @typedef {Object} ObfuscatorOptions
+ * @property {boolean} [ObfuscatorOptions.formatting=true]
+ * @property {boolean} [ObfuscatorOptions.subdocs=true]
+ * @property {boolean} [ObfuscatorOptions.yxml=true] Whether to obfuscate nodeName / hookName
+ */
+
+/**
+ * @param {ObfuscatorOptions} obfuscator
+ */
+const createObfuscator = ({ formatting = true, subdocs = true, yxml = true } = {}) => {
+  let i = 0
+  const mapKeyCache = map.create()
+  const nodeNameCache = map.create()
+  const formattingKeyCache = map.create()
+  const formattingValueCache = map.create()
+  formattingValueCache.set(null, null) // end of a formatting range should always be the end of a formatting range
+  /**
+   * @param {Item|GC|Skip} block
+   * @return {Item|GC|Skip}
+   */
+  return block => {
+    switch (block.constructor) {
+      case GC:
+      case Skip:
+        return block
+      case Item: {
+        const item = /** @type {Item} */ (block)
+        const content = item.content
+        switch (content.constructor) {
+          case ContentDeleted:
+            break
+          case ContentType: {
+            if (yxml) {
+              const type = /** @type {ContentType} */ (content).type
+              if (type instanceof YXmlElement) {
+                type.nodeName = map.setIfUndefined(nodeNameCache, type.nodeName, () => 'node-' + i)
+              }
+              if (type instanceof YXmlHook) {
+                type.hookName = map.setIfUndefined(nodeNameCache, type.hookName, () => 'hook-' + i)
+              }
+            }
+            break
+          }
+          case ContentAny: {
+            const c = /** @type {ContentAny} */ (content)
+            c.arr = c.arr.map(() => i)
+            break
+          }
+          case ContentBinary: {
+            const c = /** @type {ContentBinary} */ (content)
+            c.content = new Uint8Array([i])
+            break
+          }
+          case ContentDoc: {
+            const c = /** @type {ContentDoc} */ (content)
+            if (subdocs) {
+              c.opts = {}
+              c.doc.guid = i + ''
+            }
+            break
+          }
+          case ContentEmbed: {
+            const c = /** @type {ContentEmbed} */ (content)
+            c.embed = {}
+            break
+          }
+          case ContentFormat: {
+            const c = /** @type {ContentFormat} */ (content)
+            if (formatting) {
+              c.key = map.setIfUndefined(formattingKeyCache, c.key, () => i + '')
+              c.value = map.setIfUndefined(formattingValueCache, c.value, () => ({ i }))
+            }
+            break
+          }
+          case ContentJSON: {
+            const c = /** @type {ContentJSON} */ (content)
+            c.arr = c.arr.map(() => i)
+            break
+          }
+          case ContentString: {
+            const c = /** @type {ContentString} */ (content)
+            c.str = string.repeat((i % 10) + '', c.str.length)
+            break
+          }
+          default:
+            // unknown content type
+            error.unexpectedCase()
+        }
+        if (item.parentSub) {
+          item.parentSub = map.setIfUndefined(mapKeyCache, item.parentSub, () => i + '')
+        }
+        i++
+        return block
+      }
+      default:
+        // unknown block-type
+        error.unexpectedCase()
+    }
+  }
+}
+
+/**
+ * This function obfuscates the content of a Yjs update. This is useful to share
+ * buggy Yjs documents while significantly limiting the possibility that a
+ * developer can on the user. Note that it might still be possible to deduce
+ * some information by analyzing the "structure" of the document or by analyzing
+ * the typing behavior using the CRDT-related metadata that is still kept fully
+ * intact.
+ *
+ * @param {Uint8Array} update
+ * @param {ObfuscatorOptions} [opts]
+ */
+export const obfuscateUpdate = (update, opts) => convertUpdateFormat(update, createObfuscator(opts), UpdateDecoderV1, UpdateEncoderV1)
+
+/**
+ * @param {Uint8Array} update
+ * @param {ObfuscatorOptions} [opts]
+ */
+export const obfuscateUpdateV2 = (update, opts) => convertUpdateFormat(update, createObfuscator(opts), UpdateDecoderV2, UpdateEncoderV2)
+
+/**
+ * @param {Uint8Array} update
+ */
+export const convertUpdateFormatV1ToV2 = update => convertUpdateFormat(update, f.id, UpdateDecoderV1, UpdateEncoderV2)
+
+/**
+ * @param {Uint8Array} update
+ */
+export const convertUpdateFormatV2ToV1 = update => convertUpdateFormat(update, f.id, UpdateDecoderV2, UpdateEncoderV1)
--- a/test.html
+++ b/test.html
@ -0,0 +1,9 @@
+<!DOCTYPE html>
+<html>
+<head>
+  <title>Testing Yjs</title>
+</head>
+<body>
+  <script type="module" src="./dist/tests.js"></script>
+</body>
+</html>
--- a/tests/compatibility.tests.js
+++ b/tests/compatibility.tests.js
--- a/tests/doc.tests.js
+++ b/tests/doc.tests.js
@ -0,0 +1,329 @@
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testAfterTransactionRecursion = _tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment('')
+  ydoc.on('afterTransaction', tr => {
+    if (tr.origin === 'test') {
+      yxml.toJSON()
+    }
+  })
+  ydoc.transact(_tr => {
+    for (let i = 0; i < 15000; i++) {
+      yxml.push([new Y.XmlText('a')])
+    }
+  }, 'test')
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testOriginInTransaction = _tc => {
+  const doc = new Y.Doc()
+  const ytext = doc.getText()
+  /**
+   * @type {Array<string>}
+   */
+  const origins = []
+  doc.on('afterTransaction', (tr) => {
+    origins.push(tr.origin)
+    if (origins.length <= 1) {
+      ytext.toDelta(Y.snapshot(doc)) // adding a snapshot forces toDelta to create a cleanup transaction
+      doc.transact(() => {
+        ytext.insert(0, 'a')
+      }, 'nested')
+    }
+  })
+  doc.transact(() => {
+    ytext.insert(0, '0')
+  }, 'first')
+  t.compareArrays(origins, ['first', 'cleanup', 'nested'])
+}
+
+/**
+ * Client id should be changed when an instance receives updates from another client using the same client id.
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testClientIdDuplicateChange = _tc => {
+  const doc1 = new Y.Doc()
+  doc1.clientID = 0
+  const doc2 = new Y.Doc()
+  doc2.clientID = 0
+  t.assert(doc2.clientID === doc1.clientID)
+  doc1.getArray('a').insert(0, [1, 2])
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc1))
+  t.assert(doc2.clientID !== doc1.clientID)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testGetTypeEmptyId = _tc => {
+  const doc1 = new Y.Doc()
+  doc1.getText('').insert(0, 'h')
+  doc1.getText().insert(1, 'i')
+  const doc2 = new Y.Doc()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc1))
+  t.assert(doc2.getText().toString() === 'hi')
+  t.assert(doc2.getText('').toString() === 'hi')
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testToJSON = _tc => {
+  const doc = new Y.Doc()
+  t.compare(doc.toJSON(), {}, 'doc.toJSON yields empty object')
+
+  const arr = doc.getArray('array')
+  arr.push(['test1'])
+
+  const map = doc.getMap('map')
+  map.set('k1', 'v1')
+  const map2 = new Y.Map()
+  map.set('k2', map2)
+  map2.set('m2k1', 'm2v1')
+
+  t.compare(doc.toJSON(), {
+    array: ['test1'],
+    map: {
+      k1: 'v1',
+      k2: {
+        m2k1: 'm2v1'
+      }
+    }
+  }, 'doc.toJSON has array and recursive map')
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSubdoc = _tc => {
+  const doc = new Y.Doc()
+  doc.load() // doesn't do anything
+  {
+    /**
+     * @type {Array<any>|null}
+     */
+    let event = /** @type {any} */ (null)
+    doc.on('subdocs', subdocs => {
+      event = [Array.from(subdocs.added).map(x => x.guid), Array.from(subdocs.removed).map(x => x.guid), Array.from(subdocs.loaded).map(x => x.guid)]
+    })
+    const subdocs = doc.getMap('mysubdocs')
+    const docA = new Y.Doc({ guid: 'a' })
+    docA.load()
+    subdocs.set('a', docA)
+    t.compare(event, [['a'], [], ['a']])
+
+    event = null
+    subdocs.get('a').load()
+    t.assert(event === null)
+
+    event = null
+    subdocs.get('a').destroy()
+    t.compare(event, [['a'], ['a'], []])
+    subdocs.get('a').load()
+    t.compare(event, [[], [], ['a']])
+
+    subdocs.set('b', new Y.Doc({ guid: 'a', shouldLoad: false }))
+    t.compare(event, [['a'], [], []])
+    subdocs.get('b').load()
+    t.compare(event, [[], [], ['a']])
+
+    const docC = new Y.Doc({ guid: 'c' })
+    docC.load()
+    subdocs.set('c', docC)
+    t.compare(event, [['c'], [], ['c']])
+
+    t.compare(Array.from(doc.getSubdocGuids()), ['a', 'c'])
+  }
+
+  const doc2 = new Y.Doc()
+  {
+    t.compare(Array.from(doc2.getSubdocs()), [])
+    /**
+     * @type {Array<any>|null}
+     */
+    let event = /** @type {any} */ (null)
+    doc2.on('subdocs', subdocs => {
+      event = [Array.from(subdocs.added).map(d => d.guid), Array.from(subdocs.removed).map(d => d.guid), Array.from(subdocs.loaded).map(d => d.guid)]
+    })
+    Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+    t.compare(event, [['a', 'a', 'c'], [], []])
+
+    doc2.getMap('mysubdocs').get('a').load()
+    t.compare(event, [[], [], ['a']])
+
+    t.compare(Array.from(doc2.getSubdocGuids()), ['a', 'c'])
+
+    doc2.getMap('mysubdocs').delete('a')
+    t.compare(event, [[], ['a'], []])
+    t.compare(Array.from(doc2.getSubdocGuids()), ['a', 'c'])
+  }
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSubdocLoadEdgeCases = _tc => {
+  const ydoc = new Y.Doc()
+  const yarray = ydoc.getArray()
+  const subdoc1 = new Y.Doc()
+  /**
+   * @type {any}
+   */
+  let lastEvent = null
+  ydoc.on('subdocs', event => {
+    lastEvent = event
+  })
+  yarray.insert(0, [subdoc1])
+  t.assert(subdoc1.shouldLoad)
+  t.assert(subdoc1.autoLoad === false)
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc1))
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc1))
+  // destroy and check whether lastEvent adds it again to added (it shouldn't)
+  subdoc1.destroy()
+  const subdoc2 = yarray.get(0)
+  t.assert(subdoc1 !== subdoc2)
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc2))
+  t.assert(lastEvent !== null && !lastEvent.loaded.has(subdoc2))
+  // load
+  subdoc2.load()
+  t.assert(lastEvent !== null && !lastEvent.added.has(subdoc2))
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc2))
+  // apply from remote
+  const ydoc2 = new Y.Doc()
+  ydoc2.on('subdocs', event => {
+    lastEvent = event
+  })
+  Y.applyUpdate(ydoc2, Y.encodeStateAsUpdate(ydoc))
+  const subdoc3 = ydoc2.getArray().get(0)
+  t.assert(subdoc3.shouldLoad === false)
+  t.assert(subdoc3.autoLoad === false)
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc3))
+  t.assert(lastEvent !== null && !lastEvent.loaded.has(subdoc3))
+  // load
+  subdoc3.load()
+  t.assert(subdoc3.shouldLoad)
+  t.assert(lastEvent !== null && !lastEvent.added.has(subdoc3))
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc3))
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSubdocLoadEdgeCasesAutoload = _tc => {
+  const ydoc = new Y.Doc()
+  const yarray = ydoc.getArray()
+  const subdoc1 = new Y.Doc({ autoLoad: true })
+  /**
+   * @type {any}
+   */
+  let lastEvent = null
+  ydoc.on('subdocs', event => {
+    lastEvent = event
+  })
+  yarray.insert(0, [subdoc1])
+  t.assert(subdoc1.shouldLoad)
+  t.assert(subdoc1.autoLoad)
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc1))
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc1))
+  // destroy and check whether lastEvent adds it again to added (it shouldn't)
+  subdoc1.destroy()
+  const subdoc2 = yarray.get(0)
+  t.assert(subdoc1 !== subdoc2)
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc2))
+  t.assert(lastEvent !== null && !lastEvent.loaded.has(subdoc2))
+  // load
+  subdoc2.load()
+  t.assert(lastEvent !== null && !lastEvent.added.has(subdoc2))
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc2))
+  // apply from remote
+  const ydoc2 = new Y.Doc()
+  ydoc2.on('subdocs', event => {
+    lastEvent = event
+  })
+  Y.applyUpdate(ydoc2, Y.encodeStateAsUpdate(ydoc))
+  const subdoc3 = ydoc2.getArray().get(0)
+  t.assert(subdoc1.shouldLoad)
+  t.assert(subdoc1.autoLoad)
+  t.assert(lastEvent !== null && lastEvent.added.has(subdoc3))
+  t.assert(lastEvent !== null && lastEvent.loaded.has(subdoc3))
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSubdocsUndo = _tc => {
+  const ydoc = new Y.Doc()
+  const elems = ydoc.getXmlFragment()
+  const undoManager = new Y.UndoManager(elems)
+  const subdoc = new Y.Doc()
+  // @ts-ignore
+  elems.insert(0, [subdoc])
+  undoManager.undo()
+  undoManager.redo()
+  t.assert(elems.length === 1)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testLoadDocsEvent = async _tc => {
+  const ydoc = new Y.Doc()
+  t.assert(ydoc.isLoaded === false)
+  let loadedEvent = false
+  ydoc.on('load', () => {
+    loadedEvent = true
+  })
+  ydoc.emit('load', [ydoc])
+  await ydoc.whenLoaded
+  t.assert(loadedEvent)
+  t.assert(ydoc.isLoaded)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSyncDocsEvent = async _tc => {
+  const ydoc = new Y.Doc()
+  t.assert(ydoc.isLoaded === false)
+  t.assert(ydoc.isSynced === false)
+  let loadedEvent = false
+  ydoc.once('load', () => {
+    loadedEvent = true
+  })
+  let syncedEvent = false
+  ydoc.once('sync', /** @param {any} isSynced */ (isSynced) => {
+    syncedEvent = true
+    t.assert(isSynced)
+  })
+  ydoc.emit('sync', [true, ydoc])
+  await ydoc.whenLoaded
+  const oldWhenSynced = ydoc.whenSynced
+  await ydoc.whenSynced
+  t.assert(loadedEvent)
+  t.assert(syncedEvent)
+  t.assert(ydoc.isLoaded)
+  t.assert(ydoc.isSynced)
+  let loadedEvent2 = false
+  ydoc.on('load', () => {
+    loadedEvent2 = true
+  })
+  let syncedEvent2 = false
+  ydoc.on('sync', (isSynced) => {
+    syncedEvent2 = true
+    t.assert(isSynced === false)
+  })
+  ydoc.emit('sync', [false, ydoc])
+  t.assert(!loadedEvent2)
+  t.assert(syncedEvent2)
+  t.assert(ydoc.isLoaded)
+  t.assert(!ydoc.isSynced)
+  t.assert(ydoc.whenSynced !== oldWhenSynced)
+}
--- a/tests/encoding.tests.js
+++ b/tests/encoding.tests.js
@ -0,0 +1,108 @@
+import * as t from 'lib0/testing'
+import * as promise from 'lib0/promise'
+
+import {
+  contentRefs,
+  readContentBinary,
+  readContentDeleted,
+  readContentString,
+  readContentJSON,
+  readContentEmbed,
+  readContentType,
+  readContentFormat,
+  readContentAny,
+  readContentDoc,
+  Doc,
+  PermanentUserData,
+  encodeStateAsUpdate,
+  applyUpdate
+} from '../src/internals.js'
+
+import * as Y from '../src/index.js'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testStructReferences = tc => {
+  t.assert(contentRefs.length === 11)
+  t.assert(contentRefs[1] === readContentDeleted)
+  t.assert(contentRefs[2] === readContentJSON) // TODO: deprecate content json?
+  t.assert(contentRefs[3] === readContentBinary)
+  t.assert(contentRefs[4] === readContentString)
+  t.assert(contentRefs[5] === readContentEmbed)
+  t.assert(contentRefs[6] === readContentFormat)
+  t.assert(contentRefs[7] === readContentType)
+  t.assert(contentRefs[8] === readContentAny)
+  t.assert(contentRefs[9] === readContentDoc)
+  // contentRefs[10] is reserved for Skip structs
+}
+
+/**
+ * There is some custom encoding/decoding happening in PermanentUserData.
+ * This is why it landed here.
+ *
+ * @param {t.TestCase} tc
+ */
+export const testPermanentUserData = async tc => {
+  const ydoc1 = new Doc()
+  const ydoc2 = new Doc()
+  const pd1 = new PermanentUserData(ydoc1)
+  const pd2 = new PermanentUserData(ydoc2)
+  pd1.setUserMapping(ydoc1, ydoc1.clientID, 'user a')
+  pd2.setUserMapping(ydoc2, ydoc2.clientID, 'user b')
+  ydoc1.getText().insert(0, 'xhi')
+  ydoc1.getText().delete(0, 1)
+  ydoc2.getText().insert(0, 'hxxi')
+  ydoc2.getText().delete(1, 2)
+  await promise.wait(10)
+  applyUpdate(ydoc2, encodeStateAsUpdate(ydoc1))
+  applyUpdate(ydoc1, encodeStateAsUpdate(ydoc2))
+
+  // now sync a third doc with same name as doc1 and then create PermanentUserData
+  const ydoc3 = new Doc()
+  applyUpdate(ydoc3, encodeStateAsUpdate(ydoc1))
+  const pd3 = new PermanentUserData(ydoc3)
+  pd3.setUserMapping(ydoc3, ydoc3.clientID, 'user a')
+}
+
+/**
+ * Reported here: https://github.com/yjs/yjs/issues/308
+ * @param {t.TestCase} tc
+ */
+export const testDiffStateVectorOfUpdateIsEmpty = tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {any}
+   */
+  let sv = null
+  ydoc.getText().insert(0, 'a')
+  ydoc.on('update', update => {
+    sv = Y.encodeStateVectorFromUpdate(update)
+  })
+  // should produce an update with an empty state vector (because previous ops are missing)
+  ydoc.getText().insert(0, 'a')
+  t.assert(sv !== null && sv.byteLength === 1 && sv[0] === 0)
+}
+
+/**
+ * Reported here: https://github.com/yjs/yjs/issues/308
+ * @param {t.TestCase} tc
+ */
+export const testDiffStateVectorOfUpdateIgnoresSkips = tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const updates = []
+  ydoc.on('update', update => {
+    updates.push(update)
+  })
+  ydoc.getText().insert(0, 'a')
+  ydoc.getText().insert(0, 'b')
+  ydoc.getText().insert(0, 'c')
+  const update13 = Y.mergeUpdates([updates[0], updates[2]])
+  const sv = Y.encodeStateVectorFromUpdate(update13)
+  const state = Y.decodeStateVector(sv)
+  t.assert(state.get(ydoc.clientID) === 1)
+  t.assert(state.size === 1)
+}
--- a/tests/index.js
+++ b/tests/index.js
@ -0,0 +1,42 @@
+/* eslint-env node */
+
+import * as map from './y-map.tests.js'
+import * as array from './y-array.tests.js'
+import * as text from './y-text.tests.js'
+import * as xml from './y-xml.tests.js'
+import * as encoding from './encoding.tests.js'
+import * as undoredo from './undo-redo.tests.js'
+import * as compatibility from './compatibility.tests.js'
+import * as doc from './doc.tests.js'
+import * as snapshot from './snapshot.tests.js'
+import * as updates from './updates.tests.js'
+import * as relativePositions from './relativePositions.tests.js'
+
+import { runTests } from 'lib0/testing'
+import { isBrowser, isNode } from 'lib0/environment'
+import * as log from 'lib0/logging'
+import { environment } from 'lib0'
+
+if (isBrowser) {
+  log.createVConsole(document.body)
+}
+
+/**
+ * @type {any}
+ */
+const tests = {
+  doc, map, array, text, xml, encoding, undoredo, compatibility, snapshot, updates, relativePositions
+}
+
+const run = async () => {
+  if (environment.isNode) {
+    // tests.nodejs = await import('./node.tests.js')
+  }
+
+  const success = await runTests(tests)
+  /* istanbul ignore next */
+  if (isNode) {
+    process.exit(success ? 0 : 1)
+  }
+}
+run()
--- a/tests/relativePositions.tests.js
+++ b/tests/relativePositions.tests.js
@ -0,0 +1,145 @@
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+
+/**
+ * @param {Y.Text} ytext
+ */
+const checkRelativePositions = ytext => {
+  // test if all positions are encoded and restored correctly
+  for (let i = 0; i < ytext.length; i++) {
+    // for all types of associations..
+    for (let assoc = -1; assoc < 2; assoc++) {
+      const rpos = Y.createRelativePositionFromTypeIndex(ytext, i, assoc)
+      const encodedRpos = Y.encodeRelativePosition(rpos)
+      const decodedRpos = Y.decodeRelativePosition(encodedRpos)
+      const absPos = /** @type {Y.AbsolutePosition} */ (Y.createAbsolutePositionFromRelativePosition(decodedRpos, /** @type {Y.Doc} */ (ytext.doc)))
+      t.assert(absPos.index === i)
+      t.assert(absPos.assoc === assoc)
+    }
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase1 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '1')
+  ytext.insert(0, 'abc')
+  ytext.insert(0, 'z')
+  ytext.insert(0, 'y')
+  ytext.insert(0, 'x')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase2 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, 'abc')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase3 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, 'abc')
+  ytext.insert(0, '1')
+  ytext.insert(0, 'xyz')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase4 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '1')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase5 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '2')
+  ytext.insert(0, '1')
+  checkRelativePositions(ytext)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase6 = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  checkRelativePositions(ytext)
+}
+
+/**
+ * Testing https://github.com/yjs/yjs/issues/657
+ *
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionCase7 = tc => {
+  const docA = new Y.Doc()
+  const textA = docA.getText('text')
+  textA.insert(0, 'abcde')
+  // Create a relative position at index 2 in 'textA'
+  const relativePosition = Y.createRelativePositionFromTypeIndex(textA, 2)
+  // Verify that the absolutes positions on 'docA' are the same
+  const absolutePositionWithFollow =
+    Y.createAbsolutePositionFromRelativePosition(relativePosition, docA, true)
+  const absolutePositionWithoutFollow =
+    Y.createAbsolutePositionFromRelativePosition(relativePosition, docA, false)
+  t.assert(absolutePositionWithFollow?.index === 2)
+  t.assert(absolutePositionWithoutFollow?.index === 2)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionAssociationDifference = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, '2')
+  ytext.insert(0, '1')
+  const rposRight = Y.createRelativePositionFromTypeIndex(ytext, 1, 0)
+  const rposLeft = Y.createRelativePositionFromTypeIndex(ytext, 1, -1)
+  ytext.insert(1, 'x')
+  const posRight = Y.createAbsolutePositionFromRelativePosition(rposRight, ydoc)
+  const posLeft = Y.createAbsolutePositionFromRelativePosition(rposLeft, ydoc)
+  t.assert(posRight != null && posRight.index === 2)
+  t.assert(posLeft != null && posLeft.index === 1)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRelativePositionWithUndo = tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText()
+  ytext.insert(0, 'hello world')
+  const rpos = Y.createRelativePositionFromTypeIndex(ytext, 1)
+  const um = new Y.UndoManager(ytext)
+  ytext.delete(0, 6)
+  t.assert(Y.createAbsolutePositionFromRelativePosition(rpos, ydoc)?.index === 0)
+  um.undo()
+  t.assert(Y.createAbsolutePositionFromRelativePosition(rpos, ydoc)?.index === 1)
+  const posWithoutFollow = Y.createAbsolutePositionFromRelativePosition(rpos, ydoc, false)
+  console.log({ posWithoutFollow })
+  t.assert(Y.createAbsolutePositionFromRelativePosition(rpos, ydoc, false)?.index === 6)
+  const ydocClone = new Y.Doc()
+  Y.applyUpdate(ydocClone, Y.encodeStateAsUpdate(ydoc))
+  t.assert(Y.createAbsolutePositionFromRelativePosition(rpos, ydocClone)?.index === 6)
+  t.assert(Y.createAbsolutePositionFromRelativePosition(rpos, ydocClone, false)?.index === 6)
+}
--- a/tests/snapshot.tests.js
+++ b/tests/snapshot.tests.js
@ -0,0 +1,223 @@
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+import { init } from './testHelper.js'
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testBasic = _tc => {
+  const ydoc = new Y.Doc({ gc: false })
+  ydoc.getText().insert(0, 'world!')
+  const snapshot = Y.snapshot(ydoc)
+  ydoc.getText().insert(0, 'hello ')
+  const restored = Y.createDocFromSnapshot(ydoc, snapshot)
+  t.assert(restored.getText().toString() === 'world!')
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testBasicXmlAttributes = _tc => {
+  const ydoc = new Y.Doc({ gc: false })
+  const yxml = ydoc.getMap().set('el', new Y.XmlElement('div'))
+  const snapshot1 = Y.snapshot(ydoc)
+  yxml.setAttribute('a', '1')
+  const snapshot2 = Y.snapshot(ydoc)
+  yxml.setAttribute('a', '2')
+  t.compare(yxml.getAttributes(), { a: '2' })
+  t.compare(yxml.getAttributes(snapshot2), { a: '1' })
+  t.compare(yxml.getAttributes(snapshot1), {})
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testBasicRestoreSnapshot = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, ['hello'])
+  const snap = Y.snapshot(doc)
+  doc.getArray('array').insert(1, ['world'])
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['hello'])
+  t.compare(doc.getArray('array').toArray(), ['hello', 'world'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testEmptyRestoreSnapshot = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  const snap = Y.snapshot(doc)
+  snap.sv.set(9999, 0)
+  doc.getArray().insert(0, ['world'])
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray().toArray(), [])
+  t.compare(doc.getArray().toArray(), ['world'])
+
+  // now this snapshot reflects the latest state. It should still work.
+  const snap2 = Y.snapshot(doc)
+  const docRestored2 = Y.createDocFromSnapshot(doc, snap2)
+  t.compare(docRestored2.getArray().toArray(), ['world'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testRestoreSnapshotWithSubType = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, [new Y.Map()])
+  const subMap = doc.getArray('array').get(0)
+  subMap.set('key1', 'value1')
+
+  const snap = Y.snapshot(doc)
+  subMap.set('key2', 'value2')
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toJSON(), [{
+    key1: 'value1'
+  }])
+  t.compare(doc.getArray('array').toJSON(), [{
+    key1: 'value1',
+    key2: 'value2'
+  }])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testRestoreDeletedItem1 = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1', 'item2'])
+
+  const snap = Y.snapshot(doc)
+  doc.getArray('array').delete(0)
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item1', 'item2'])
+  t.compare(doc.getArray('array').toArray(), ['item2'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testRestoreLeftItem = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1'])
+  doc.getMap('map').set('test', 1)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const snap = Y.snapshot(doc)
+  doc.getArray('array').delete(1)
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item0', 'item1'])
+  t.compare(doc.getArray('array').toArray(), ['item0'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testDeletedItemsBase = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1'])
+  doc.getArray('array').delete(0)
+  const snap = Y.snapshot(doc)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), [])
+  t.compare(doc.getArray('array').toArray(), ['item0'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testDeletedItems2 = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  doc.getArray('array').insert(0, ['item1', 'item2', 'item3'])
+  doc.getArray('array').delete(1)
+  const snap = Y.snapshot(doc)
+  doc.getArray('array').insert(0, ['item0'])
+
+  const docRestored = Y.createDocFromSnapshot(doc, snap)
+
+  t.compare(docRestored.getArray('array').toArray(), ['item1', 'item3'])
+  t.compare(doc.getArray('array').toArray(), ['item0', 'item1', 'item3'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDependentChanges = tc => {
+  const { array0, array1, testConnector } = init(tc, { users: 2 })
+
+  if (!array0.doc) {
+    throw new Error('no document 0')
+  }
+  if (!array1.doc) {
+    throw new Error('no document 1')
+  }
+
+  /**
+   * @type {Y.Doc}
+   */
+  const doc0 = array0.doc
+  /**
+   * @type {Y.Doc}
+   */
+  const doc1 = array1.doc
+
+  doc0.gc = false
+  doc1.gc = false
+
+  array0.insert(0, ['user1item1'])
+  testConnector.syncAll()
+  array1.insert(1, ['user2item1'])
+  testConnector.syncAll()
+
+  const snap = Y.snapshot(array0.doc)
+
+  array0.insert(2, ['user1item2'])
+  testConnector.syncAll()
+  array1.insert(3, ['user2item2'])
+  testConnector.syncAll()
+
+  const docRestored0 = Y.createDocFromSnapshot(array0.doc, snap)
+  t.compare(docRestored0.getArray('array').toArray(), ['user1item1', 'user2item1'])
+
+  const docRestored1 = Y.createDocFromSnapshot(array1.doc, snap)
+  t.compare(docRestored1.getArray('array').toArray(), ['user1item1', 'user2item1'])
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testContainsUpdate = _tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const updates = []
+  ydoc.on('update', update => {
+    updates.push(update)
+  })
+  const yarr = ydoc.getArray()
+  const snapshot1 = Y.snapshot(ydoc)
+  yarr.insert(0, [1])
+  const snapshot2 = Y.snapshot(ydoc)
+  yarr.delete(0, 1)
+  const snapshotFinal = Y.snapshot(ydoc)
+  t.assert(!Y.snapshotContainsUpdate(snapshot1, updates[0]))
+  t.assert(!Y.snapshotContainsUpdate(snapshot2, updates[1]))
+  t.assert(Y.snapshotContainsUpdate(snapshot2, updates[0]))
+  t.assert(Y.snapshotContainsUpdate(snapshotFinal, updates[0]))
+  t.assert(Y.snapshotContainsUpdate(snapshotFinal, updates[1]))
+}
--- a/tests/testHelper.js
+++ b/tests/testHelper.js
@ -0,0 +1,454 @@
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as syncProtocol from 'y-protocols/sync'
+import * as object from 'lib0/object'
+import * as map from 'lib0/map'
+import * as Y from '../src/index.js'
+export * from '../src/index.js'
+
+if (typeof window !== 'undefined') {
+  // @ts-ignore
+  window.Y = Y // eslint-disable-line
+}
+
+/**
+ * @param {TestYInstance} y // publish message created by `y` to all other online clients
+ * @param {Uint8Array} m
+ */
+const broadcastMessage = (y, m) => {
+  if (y.tc.onlineConns.has(y)) {
+    y.tc.onlineConns.forEach(remoteYInstance => {
+      if (remoteYInstance !== y) {
+        remoteYInstance._receive(m, y)
+      }
+    })
+  }
+}
+
+export let useV2 = false
+
+export const encV1 = {
+  encodeStateAsUpdate: Y.encodeStateAsUpdate,
+  mergeUpdates: Y.mergeUpdates,
+  applyUpdate: Y.applyUpdate,
+  logUpdate: Y.logUpdate,
+  updateEventName: /** @type {'update'} */ ('update'),
+  diffUpdate: Y.diffUpdate
+}
+
+export const encV2 = {
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  mergeUpdates: Y.mergeUpdatesV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  updateEventName: /** @type {'updateV2'} */ ('updateV2'),
+  diffUpdate: Y.diffUpdateV2
+}
+
+export let enc = encV1
+
+const useV1Encoding = () => {
+  useV2 = false
+  enc = encV1
+}
+
+const useV2Encoding = () => {
+  console.error('sync protocol doesnt support v2 protocol yet, fallback to v1 encoding') // @Todo
+  useV2 = false
+  enc = encV1
+}
+
+export class TestYInstance extends Y.Doc {
+  /**
+   * @param {TestConnector} testConnector
+   * @param {number} clientID
+   */
+  constructor (testConnector, clientID) {
+    super()
+    this.userID = clientID // overwriting clientID
+    /**
+     * @type {TestConnector}
+     */
+    this.tc = testConnector
+    /**
+     * @type {Map<TestYInstance, Array<Uint8Array>>}
+     */
+    this.receiving = new Map()
+    testConnector.allConns.add(this)
+    /**
+     * The list of received updates.
+     * We are going to merge them later using Y.mergeUpdates and check if the resulting document is correct.
+     * @type {Array<Uint8Array>}
+     */
+    this.updates = []
+    // set up observe on local model
+    this.on(enc.updateEventName, /** @param {Uint8Array} update @param {any} origin */ (update, origin) => {
+      if (origin !== testConnector) {
+        const encoder = encoding.createEncoder()
+        syncProtocol.writeUpdate(encoder, update)
+        broadcastMessage(this, encoding.toUint8Array(encoder))
+      }
+      this.updates.push(update)
+    })
+    this.connect()
+  }
+
+  /**
+   * Disconnect from TestConnector.
+   */
+  disconnect () {
+    this.receiving = new Map()
+    this.tc.onlineConns.delete(this)
+  }
+
+  /**
+   * Append yourself to the list of known Y instances in testconnector.
+   * Also initiate sync with all clients.
+   */
+  connect () {
+    if (!this.tc.onlineConns.has(this)) {
+      this.tc.onlineConns.add(this)
+      const encoder = encoding.createEncoder()
+      syncProtocol.writeSyncStep1(encoder, this)
+      // publish SyncStep1
+      broadcastMessage(this, encoding.toUint8Array(encoder))
+      this.tc.onlineConns.forEach(remoteYInstance => {
+        if (remoteYInstance !== this) {
+          // remote instance sends instance to this instance
+          const encoder = encoding.createEncoder()
+          syncProtocol.writeSyncStep1(encoder, remoteYInstance)
+          this._receive(encoding.toUint8Array(encoder), remoteYInstance)
+        }
+      })
+    }
+  }
+
+  /**
+   * Receive a message from another client. This message is only appended to the list of receiving messages.
+   * TestConnector decides when this client actually reads this message.
+   *
+   * @param {Uint8Array} message
+   * @param {TestYInstance} remoteClient
+   */
+  _receive (message, remoteClient) {
+    map.setIfUndefined(this.receiving, remoteClient, () => /** @type {Array<Uint8Array>} */ ([])).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
+  // choose an encoding approach at random
+  if (prng.bool(gen)) {
+    useV2Encoding()
+  } else {
+    useV1Encoding()
+  }
+
+  const testConnector = new TestConnector(gen)
+  result.testConnector = testConnector
+  for (let i = 0; i < users; i++) {
+    const y = testConnector.createY(i)
+    y.clientID = i
+    result.users.push(y)
+    result['array' + i] = y.getArray('array')
+    result['map' + i] = y.getMap('map')
+    result['xml' + i] = y.get('xml', Y.XmlElement)
+    result['text' + i] = y.getText('text')
+  }
+  testConnector.syncAll()
+  result.testObjects = result.users.map(initTestObject || (() => null))
+  useV1Encoding()
+  return /** @type {any} */ (result)
+}
+
+/**
+ * 1. reconnect and flush all
+ * 2. user 0 gc
+ * 3. get type content
+ * 4. disconnect & reconnect all (so gc is propagated)
+ * 5. compare os, ds, ss
+ *
+ * @param {Array<TestYInstance>} users
+ */
+export const compare = users => {
+  users.forEach(u => u.connect())
+  while (users[0].tc.flushAllMessages()) {} // eslint-disable-line
+  // For each document, merge all received document updates with Y.mergeUpdates and create a new document which will be added to the list of "users"
+  // This ensures that mergeUpdates works correctly
+  const mergedDocs = users.map(user => {
+    const ydoc = new Y.Doc()
+    enc.applyUpdate(ydoc, enc.mergeUpdates(user.updates))
+    return ydoc
+  })
+  users.push(.../** @type {any} */(mergedDocs))
+  const userArrayValues = users.map(u => u.getArray('array').toJSON())
+  const userMapValues = users.map(u => u.getMap('map').toJSON())
+  const userXmlValues = users.map(u => u.get('xml', Y.XmlElement).toString())
+  const userTextValues = users.map(u => u.getText('text').toDelta())
+  for (const u of users) {
+    t.assert(u.store.pendingDs === null)
+    t.assert(u.store.pendingStructs === null)
+  }
+  // Test Array iterator
+  t.compare(users[0].getArray('array').toArray(), Array.from(users[0].getArray('array')))
+  // Test Map iterator
+  const ymapkeys = Array.from(users[0].getMap('map').keys())
+  t.assert(ymapkeys.length === Object.keys(userMapValues[0]).length)
+  ymapkeys.forEach(key => t.assert(object.hasProperty(userMapValues[0], key)))
+  /**
+   * @type {Object<string,any>}
+   */
+  const mapRes = {}
+  for (const [k, v] of users[0].getMap('map')) {
+    mapRes[k] = v instanceof Y.AbstractType ? v.toJSON() : v
+  }
+  t.compare(userMapValues[0], mapRes)
+  // Compare all users
+  for (let i = 0; i < users.length - 1; i++) {
+    t.compare(userArrayValues[i].length, users[i].getArray('array').length)
+    t.compare(userArrayValues[i], userArrayValues[i + 1])
+    t.compare(userMapValues[i], userMapValues[i + 1])
+    t.compare(userXmlValues[i], userXmlValues[i + 1])
+    t.compare(userTextValues[i].map(/** @param {any} a */ a => typeof a.insert === 'string' ? a.insert : ' ').join('').length, users[i].getText('text').length)
+    t.compare(userTextValues[i], userTextValues[i + 1], '', (_constructor, a, b) => {
+      if (a instanceof Y.AbstractType) {
+        t.compare(a.toJSON(), b.toJSON())
+      } else if (a !== b) {
+        t.fail('Deltas dont match')
+      }
+      return true
+    })
+    t.compare(Y.encodeStateVector(users[i]), Y.encodeStateVector(users[i + 1]))
+    Y.equalDeleteSets(Y.createDeleteSetFromStructStore(users[i].store), Y.createDeleteSetFromStructStore(users[i + 1].store))
+    compareStructStores(users[i].store, users[i + 1].store)
+    t.compare(Y.encodeSnapshot(Y.snapshot(users[i])), Y.encodeSnapshot(Y.snapshot(users[i + 1])))
+  }
+  users.map(u => u.destroy())
+}
+
+/**
+ * @param {Y.Item?} a
+ * @param {Y.Item?} b
+ * @return {boolean}
+ */
+export const compareItemIDs = (a, b) => a === b || (a !== null && b != null && Y.compareIDs(a.id, b.id))
+
+/**
+ * @param {import('../src/internals.js').StructStore} ss1
+ * @param {import('../src/internals.js').StructStore} ss2
+ */
+export const compareStructStores = (ss1, ss2) => {
+  t.assert(ss1.clients.size === ss2.clients.size)
+  for (const [client, structs1] of ss1.clients) {
+    const structs2 = /** @type {Array<Y.AbstractStruct>} */ (ss2.clients.get(client))
+    t.assert(structs2 !== undefined && structs1.length === structs2.length)
+    for (let i = 0; i < structs1.length; i++) {
+      const s1 = structs1[i]
+      const s2 = structs2[i]
+      // checks for abstract struct
+      if (
+        s1.constructor !== s2.constructor ||
+        !Y.compareIDs(s1.id, s2.id) ||
+        s1.deleted !== s2.deleted ||
+        // @ts-ignore
+        s1.length !== s2.length
+      ) {
+        t.fail('Structs dont match')
+      }
+      if (s1 instanceof Y.Item) {
+        if (
+          !(s2 instanceof Y.Item) ||
+          !((s1.left === null && s2.left === null) || (s1.left !== null && s2.left !== null && Y.compareIDs(s1.left.lastId, s2.left.lastId))) ||
+          !compareItemIDs(s1.right, s2.right) ||
+          !Y.compareIDs(s1.origin, s2.origin) ||
+          !Y.compareIDs(s1.rightOrigin, s2.rightOrigin) ||
+          s1.parentSub !== s2.parentSub
+        ) {
+          return t.fail('Items dont match')
+        }
+        // make sure that items are connected correctly
+        t.assert(s1.left === null || s1.left.right === s1)
+        t.assert(s1.right === null || s1.right.left === s1)
+        t.assert(s2.left === null || s2.left.right === s2)
+        t.assert(s2.right === null || s2.right.left === s2)
+      }
+    }
+  }
+}
+
+/**
+ * @template T
+ * @callback InitTestObjectCallback
+ * @param {TestYInstance} y
+ * @return {T}
+ */
+
+/**
+ * @template T
+ * @param {t.TestCase} tc
+ * @param {Array<function(Y.Doc,prng.PRNG,T):void>} mods
+ * @param {number} iterations
+ * @param {InitTestObjectCallback<T>} [initTestObject]
+ */
+export const applyRandomTests = (tc, mods, iterations, initTestObject) => {
+  const gen = tc.prng
+  const result = init(tc, { users: 5 }, initTestObject)
+  const { testConnector, users } = result
+  for (let i = 0; i < iterations; i++) {
+    if (prng.int32(gen, 0, 100) <= 2) {
+      // 2% chance to disconnect/reconnect a random user
+      if (prng.bool(gen)) {
+        testConnector.disconnectRandom()
+      } else {
+        testConnector.reconnectRandom()
+      }
+    } else if (prng.int32(gen, 0, 100) <= 1) {
+      // 1% chance to flush all
+      testConnector.flushAllMessages()
+    } else if (prng.int32(gen, 0, 100) <= 50) {
+      // 50% chance to flush a random message
+      testConnector.flushRandomMessage()
+    }
+    const user = prng.int32(gen, 0, users.length - 1)
+    const test = prng.oneOf(gen, mods)
+    test(users[user], gen, result.testObjects[user])
+  }
+  compare(users)
+  return result
+}
--- a/tests/undo-redo.tests.js
+++ b/tests/undo-redo.tests.js
@ -0,0 +1,813 @@
+import { init } from './testHelper.js' // eslint-disable-line
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+
+export const testInconsistentFormat = () => {
+  /**
+   * @param {Y.Doc} ydoc
+   */
+  const testYjsMerge = ydoc => {
+    const content = /** @type {Y.XmlText} */ (ydoc.get('text', Y.XmlText))
+    content.format(0, 6, { bold: null })
+    content.format(6, 4, { type: 'text' })
+    t.compare(content.toDelta(), [
+      {
+        attributes: { type: 'text' },
+        insert: 'Merge Test'
+      },
+      {
+        attributes: { type: 'text', italic: true },
+        insert: ' After'
+      }
+    ])
+  }
+  const initializeYDoc = () => {
+    const yDoc = new Y.Doc({ gc: false })
+
+    const content = /** @type {Y.XmlText} */ (yDoc.get('text', Y.XmlText))
+    content.insert(0, ' After', { type: 'text', italic: true })
+    content.insert(0, 'Test', { type: 'text' })
+    content.insert(0, 'Merge ', { type: 'text', bold: true })
+    return yDoc
+  }
+  {
+    const yDoc = initializeYDoc()
+    testYjsMerge(yDoc)
+  }
+  {
+    const initialYDoc = initializeYDoc()
+    const yDoc = new Y.Doc({ gc: false })
+    Y.applyUpdate(yDoc, Y.encodeStateAsUpdate(initialYDoc))
+    testYjsMerge(yDoc)
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInfiniteCaptureTimeout = tc => {
+  const { array0 } = init(tc, { users: 3 })
+  const undoManager = new Y.UndoManager(array0, { captureTimeout: Number.MAX_VALUE })
+  array0.push([1, 2, 3])
+  undoManager.stopCapturing()
+  array0.push([4, 5, 6])
+  undoManager.undo()
+  t.compare(array0.toArray(), [1, 2, 3])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoText = tc => {
+  const { testConnector, text0, text1 } = init(tc, { users: 3 })
+  const undoManager = new Y.UndoManager(text0)
+
+  // items that are added & deleted in the same transaction won't be undo
+  text0.insert(0, 'test')
+  text0.delete(0, 4)
+  undoManager.undo()
+  t.assert(text0.toString() === '')
+
+  // follow redone items
+  text0.insert(0, 'a')
+  undoManager.stopCapturing()
+  text0.delete(0, 1)
+  undoManager.stopCapturing()
+  undoManager.undo()
+  t.assert(text0.toString() === 'a')
+  undoManager.undo()
+  t.assert(text0.toString() === '')
+
+  text0.insert(0, 'abc')
+  text1.insert(0, 'xyz')
+  testConnector.syncAll()
+  undoManager.undo()
+  t.assert(text0.toString() === 'xyz')
+  undoManager.redo()
+  t.assert(text0.toString() === 'abcxyz')
+  testConnector.syncAll()
+  text1.delete(0, 1)
+  testConnector.syncAll()
+  undoManager.undo()
+  t.assert(text0.toString() === 'xyz')
+  undoManager.redo()
+  t.assert(text0.toString() === 'bcxyz')
+  // test marks
+  text0.format(1, 3, { bold: true })
+  t.compare(text0.toDelta(), [{ insert: 'b' }, { insert: 'cxy', attributes: { bold: true } }, { insert: 'z' }])
+  undoManager.undo()
+  t.compare(text0.toDelta(), [{ insert: 'bcxyz' }])
+  undoManager.redo()
+  t.compare(text0.toDelta(), [{ insert: 'b' }, { insert: 'cxy', attributes: { bold: true } }, { insert: 'z' }])
+}
+
+/**
+ * Test case to fix #241
+ * @param {t.TestCase} _tc
+ */
+export const testEmptyTypeScope = _tc => {
+  const ydoc = new Y.Doc()
+  const um = new Y.UndoManager([], { doc: ydoc })
+  const yarray = ydoc.getArray()
+  um.addToScope(yarray)
+  yarray.insert(0, [1])
+  um.undo()
+  t.assert(yarray.length === 0)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testRejectUpdateExample = _tc => {
+  const tmpydoc1 = new Y.Doc()
+  tmpydoc1.getArray('restricted').insert(0, [1])
+  tmpydoc1.getArray('public').insert(0, [1])
+  const update1 = Y.encodeStateAsUpdate(tmpydoc1)
+  const tmpydoc2 = new Y.Doc()
+  tmpydoc2.getArray('public').insert(0, [2])
+  const update2 = Y.encodeStateAsUpdate(tmpydoc2)
+
+  const ydoc = new Y.Doc()
+  const restrictedType = ydoc.getArray('restricted')
+
+  /**
+   * Assume this function handles incoming updates via a communication channel like websockets.
+   * Changes to the `ydoc.getMap('restricted')` type should be rejected.
+   *
+   * - set up undo manager on the restricted types
+   * - cache pending* updates from the Ydoc to avoid certain attacks
+   * - apply received update and check whether the restricted type (or any of its children) has been changed.
+   * - catch errors that might try to circumvent the restrictions
+   * - undo changes on restricted types
+   * - reapply pending* updates
+   *
+   * @param {Uint8Array} update
+   */
+  const updateHandler = (update) => {
+    // don't handle changes of the local undo manager, which is used to undo invalid changes
+    const um = new Y.UndoManager(restrictedType, { trackedOrigins: new Set(['remote change']) })
+    const beforePendingDs = ydoc.store.pendingDs
+    const beforePendingStructs = ydoc.store.pendingStructs?.update
+    try {
+      Y.applyUpdate(ydoc, update, 'remote change')
+    } finally {
+      while (um.undoStack.length) {
+        um.undo()
+      }
+      um.destroy()
+      ydoc.store.pendingDs = beforePendingDs
+      ydoc.store.pendingStructs = null
+      if (beforePendingStructs) {
+        Y.applyUpdateV2(ydoc, beforePendingStructs)
+      }
+    }
+  }
+  updateHandler(update1)
+  updateHandler(update2)
+  t.assert(restrictedType.length === 0)
+  t.assert(ydoc.getArray('public').length === 2)
+}
+
+/**
+ * Test case to fix #241
+ * @param {t.TestCase} _tc
+ */
+export const testGlobalScope = _tc => {
+  const ydoc = new Y.Doc()
+  const um = new Y.UndoManager(ydoc)
+  const yarray = ydoc.getArray()
+  yarray.insert(0, [1])
+  um.undo()
+  t.assert(yarray.length === 0)
+}
+
+/**
+ * Test case to fix #241
+ * @param {t.TestCase} _tc
+ */
+export const testDoubleUndo = _tc => {
+  const doc = new Y.Doc()
+  const text = doc.getText()
+  text.insert(0, '1221')
+
+  const manager = new Y.UndoManager(text)
+
+  text.insert(2, '3')
+  text.insert(3, '3')
+
+  manager.undo()
+  manager.undo()
+
+  text.insert(2, '3')
+
+  t.compareStrings(text.toString(), '12321')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoMap = tc => {
+  const { testConnector, map0, map1 } = init(tc, { users: 2 })
+  map0.set('a', 0)
+  const undoManager = new Y.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 Y.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 Y.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 Y.UndoManager(text0)
+  let counter = 0
+  let receivedMetadata = -1
+  undoManager.on('stack-item-added', /** @param {any} event */ event => {
+    t.assert(event.type != null)
+    t.assert(event.changedParentTypes != null && event.changedParentTypes.has(text0))
+    event.stackItem.meta.set('test', counter++)
+  })
+  undoManager.on('stack-item-popped', /** @param {any} event */ event => {
+    t.assert(event.type != null)
+    t.assert(event.changedParentTypes != null && event.changedParentTypes.has(text0))
+    receivedMetadata = event.stackItem.meta.get('test')
+  })
+  text0.insert(0, 'abc')
+  undoManager.undo()
+  t.assert(receivedMetadata === 0)
+  undoManager.redo()
+  t.assert(receivedMetadata === 1)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTrackClass = tc => {
+  const { users, text0 } = init(tc, { users: 3 })
+  // only track origins that are numbers
+  const undoManager = new Y.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 Y.UndoManager(text0)
+  const undoManagerBoth = new Y.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 testUndoInEmbed = tc => {
+  const { text0 } = init(tc, { users: 3 })
+  const undoManager = new Y.UndoManager(text0)
+  const nestedText = new Y.Text('initial text')
+  undoManager.stopCapturing()
+  text0.insertEmbed(0, nestedText, { bold: true })
+  t.assert(nestedText.toString() === 'initial text')
+  undoManager.stopCapturing()
+  nestedText.delete(0, nestedText.length)
+  nestedText.insert(0, 'other text')
+  t.assert(nestedText.toString() === 'other text')
+  undoManager.undo()
+  t.assert(nestedText.toString() === 'initial text')
+  undoManager.undo()
+  t.assert(text0.length === 0)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testUndoDeleteFilter = tc => {
+  /**
+   * @type {Y.Array<any>}
+   */
+  const array0 = /** @type {any} */ (init(tc, { users: 3 }).array0)
+  const undoManager = new Y.UndoManager(array0, { deleteFilter: item => !(item instanceof Y.Item) || (item.content instanceof Y.ContentType && item.content.type._map.size === 0) })
+  const map0 = new Y.Map()
+  map0.set('hi', 1)
+  const map1 = new Y.Map()
+  array0.insert(0, [map0, map1])
+  undoManager.undo()
+  t.assert(array0.length === 1)
+  array0.get(0)
+  t.assert(Array.from(array0.get(0).keys()).length === 1)
+}
+
+/**
+ * This issue has been reported in https://discuss.yjs.dev/t/undomanager-with-external-updates/454/6
+ * @param {t.TestCase} _tc
+ */
+export const testUndoUntilChangePerformed = _tc => {
+  const doc = new Y.Doc()
+  const doc2 = new Y.Doc()
+  doc.on('update', update => Y.applyUpdate(doc2, update))
+  doc2.on('update', update => Y.applyUpdate(doc, update))
+
+  const yArray = doc.getArray('array')
+  const yArray2 = doc2.getArray('array')
+  const yMap = new Y.Map()
+  yMap.set('hello', 'world')
+  yArray.push([yMap])
+  const yMap2 = new Y.Map()
+  yMap2.set('key', 'value')
+  yArray.push([yMap2])
+
+  const undoManager = new Y.UndoManager([yArray], { trackedOrigins: new Set([doc.clientID]) })
+  const undoManager2 = new Y.UndoManager([doc2.get('array')], { trackedOrigins: new Set([doc2.clientID]) })
+
+  Y.transact(doc, () => yMap2.set('key', 'value modified'), doc.clientID)
+  undoManager.stopCapturing()
+  Y.transact(doc, () => yMap.set('hello', 'world modified'), doc.clientID)
+  Y.transact(doc2, () => yArray2.delete(0), doc2.clientID)
+  undoManager2.undo()
+  undoManager.undo()
+  t.compareStrings(yMap2.get('key'), 'value')
+}
+
+/**
+ * This issue has been reported in https://github.com/yjs/yjs/issues/317
+ * @param {t.TestCase} _tc
+ */
+export const testUndoNestedUndoIssue = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  const design = doc.getMap()
+  const undoManager = new Y.UndoManager(design, { captureTimeout: 0 })
+
+  /**
+   * @type {Y.Map<any>}
+   */
+  const text = new Y.Map()
+
+  const blocks1 = new Y.Array()
+  const blocks1block = new Y.Map()
+
+  doc.transact(() => {
+    blocks1block.set('text', 'Type Something')
+    blocks1.push([blocks1block])
+    text.set('blocks', blocks1block)
+    design.set('text', text)
+  })
+
+  const blocks2 = new Y.Array()
+  const blocks2block = new Y.Map()
+  doc.transact(() => {
+    blocks2block.set('text', 'Something')
+    blocks2.push([blocks2block])
+    text.set('blocks', blocks2block)
+  })
+
+  const blocks3 = new Y.Array()
+  const blocks3block = new Y.Map()
+  doc.transact(() => {
+    blocks3block.set('text', 'Something Else')
+    blocks3.push([blocks3block])
+    text.set('blocks', blocks3block)
+  })
+
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Type Something' } } })
+  undoManager.undo()
+  t.compare(design.toJSON(), { })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Type Something' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something' } } })
+  undoManager.redo()
+  t.compare(design.toJSON(), { text: { blocks: { text: 'Something Else' } } })
+}
+
+/**
+ * This issue has been reported in https://github.com/yjs/yjs/issues/355
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testConsecutiveRedoBug = _tc => {
+  const doc = new Y.Doc()
+  const yRoot = doc.getMap()
+  const undoMgr = new Y.UndoManager(yRoot)
+
+  let yPoint = new Y.Map()
+  yPoint.set('x', 0)
+  yPoint.set('y', 0)
+  yRoot.set('a', yPoint)
+  undoMgr.stopCapturing()
+
+  yPoint.set('x', 100)
+  yPoint.set('y', 100)
+  undoMgr.stopCapturing()
+
+  yPoint.set('x', 200)
+  yPoint.set('y', 200)
+  undoMgr.stopCapturing()
+
+  yPoint.set('x', 300)
+  yPoint.set('y', 300)
+  undoMgr.stopCapturing()
+
+  t.compare(yPoint.toJSON(), { x: 300, y: 300 })
+
+  undoMgr.undo() // x=200, y=200
+  t.compare(yPoint.toJSON(), { x: 200, y: 200 })
+  undoMgr.undo() // x=100, y=100
+  t.compare(yPoint.toJSON(), { x: 100, y: 100 })
+  undoMgr.undo() // x=0, y=0
+  t.compare(yPoint.toJSON(), { x: 0, y: 0 })
+  undoMgr.undo() // nil
+  t.compare(yRoot.get('a'), undefined)
+
+  undoMgr.redo() // x=0, y=0
+  yPoint = yRoot.get('a')
+
+  t.compare(yPoint.toJSON(), { x: 0, y: 0 })
+  undoMgr.redo() // x=100, y=100
+  t.compare(yPoint.toJSON(), { x: 100, y: 100 })
+  undoMgr.redo() // x=200, y=200
+  t.compare(yPoint.toJSON(), { x: 200, y: 200 })
+  undoMgr.redo() // expected x=300, y=300, actually nil
+  t.compare(yPoint.toJSON(), { x: 300, y: 300 })
+}
+
+/**
+ * This issue has been reported in https://github.com/yjs/yjs/issues/304
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testUndoXmlBug = _tc => {
+  const origin = 'origin'
+  const doc = new Y.Doc()
+  const fragment = doc.getXmlFragment('t')
+  const undoManager = new Y.UndoManager(fragment, {
+    captureTimeout: 0,
+    trackedOrigins: new Set([origin])
+  })
+
+  // create element
+  doc.transact(() => {
+    const e = new Y.XmlElement('test-node')
+    e.setAttribute('a', '100')
+    e.setAttribute('b', '0')
+    fragment.insert(fragment.length, [e])
+  }, origin)
+
+  // change one attribute
+  doc.transact(() => {
+    const e = fragment.get(0)
+    e.setAttribute('a', '200')
+  }, origin)
+
+  // change both attributes
+  doc.transact(() => {
+    const e = fragment.get(0)
+    e.setAttribute('a', '180')
+    e.setAttribute('b', '50')
+  }, origin)
+
+  undoManager.undo()
+  undoManager.undo()
+  undoManager.undo()
+
+  undoManager.redo()
+  undoManager.redo()
+  undoManager.redo()
+  t.compare(fragment.toString(), '<test-node a="180" b="50"></test-node>')
+}
+
+/**
+ * This issue has been reported in https://github.com/yjs/yjs/issues/343
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testUndoBlockBug = _tc => {
+  const doc = new Y.Doc({ gc: false })
+  const design = doc.getMap()
+
+  const undoManager = new Y.UndoManager(design, { captureTimeout: 0 })
+
+  const text = new Y.Map()
+
+  const blocks1 = new Y.Array()
+  const blocks1block = new Y.Map()
+  doc.transact(() => {
+    blocks1block.set('text', '1')
+    blocks1.push([blocks1block])
+
+    text.set('blocks', blocks1block)
+    design.set('text', text)
+  })
+
+  const blocks2 = new Y.Array()
+  const blocks2block = new Y.Map()
+  doc.transact(() => {
+    blocks2block.set('text', '2')
+    blocks2.push([blocks2block])
+    text.set('blocks', blocks2block)
+  })
+
+  const blocks3 = new Y.Array()
+  const blocks3block = new Y.Map()
+  doc.transact(() => {
+    blocks3block.set('text', '3')
+    blocks3.push([blocks3block])
+    text.set('blocks', blocks3block)
+  })
+
+  const blocks4 = new Y.Array()
+  const blocks4block = new Y.Map()
+  doc.transact(() => {
+    blocks4block.set('text', '4')
+    blocks4.push([blocks4block])
+    text.set('blocks', blocks4block)
+  })
+
+  // {"text":{"blocks":{"text":"4"}}}
+  undoManager.undo() // {"text":{"blocks":{"3"}}}
+  undoManager.undo() // {"text":{"blocks":{"text":"2"}}}
+  undoManager.undo() // {"text":{"blocks":{"text":"1"}}}
+  undoManager.undo() // {}
+  undoManager.redo() // {"text":{"blocks":{"text":"1"}}}
+  undoManager.redo() // {"text":{"blocks":{"text":"2"}}}
+  undoManager.redo() // {"text":{"blocks":{"text":"3"}}}
+  undoManager.redo() // {"text":{}}
+  t.compare(design.toJSON(), { text: { blocks: { text: '4' } } })
+}
+
+/**
+ * Undo text formatting delete should not corrupt peer state.
+ *
+ * @see https://github.com/yjs/yjs/issues/392
+ * @param {t.TestCase} _tc
+ */
+export const testUndoDeleteTextFormat = _tc => {
+  const doc = new Y.Doc()
+  const text = doc.getText()
+  text.insert(0, 'Attack ships on fire off the shoulder of Orion.')
+  const doc2 = new Y.Doc()
+  const text2 = doc2.getText()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+  const undoManager = new Y.UndoManager(text)
+
+  text.format(13, 7, { bold: true })
+  undoManager.stopCapturing()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+
+  text.format(16, 4, { bold: null })
+  undoManager.stopCapturing()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+
+  undoManager.undo()
+  Y.applyUpdate(doc2, Y.encodeStateAsUpdate(doc))
+
+  const expect = [
+    { insert: 'Attack ships ' },
+    {
+      insert: 'on fire',
+      attributes: { bold: true }
+    },
+    { insert: ' off the shoulder of Orion.' }
+  ]
+  t.compare(text.toDelta(), expect)
+  t.compare(text2.toDelta(), expect)
+}
+
+/**
+ * Undo text formatting delete should not corrupt peer state.
+ *
+ * @see https://github.com/yjs/yjs/issues/392
+ * @param {t.TestCase} _tc
+ */
+export const testBehaviorOfIgnoreremotemapchangesProperty = _tc => {
+  const doc = new Y.Doc()
+  const doc2 = new Y.Doc()
+  doc.on('update', update => Y.applyUpdate(doc2, update, doc))
+  doc2.on('update', update => Y.applyUpdate(doc, update, doc2))
+  const map1 = doc.getMap()
+  const map2 = doc2.getMap()
+  const um1 = new Y.UndoManager(map1, { ignoreRemoteMapChanges: true })
+  map1.set('x', 1)
+  map2.set('x', 2)
+  map1.set('x', 3)
+  map2.set('x', 4)
+  um1.undo()
+  t.assert(map1.get('x') === 2)
+  t.assert(map2.get('x') === 2)
+}
+
+/**
+ * Special deletion case.
+ *
+ * @see https://github.com/yjs/yjs/issues/447
+ * @param {t.TestCase} _tc
+ */
+export const testSpecialDeletionCase = _tc => {
+  const origin = 'undoable'
+  const doc = new Y.Doc()
+  const fragment = doc.getXmlFragment()
+  const undoManager = new Y.UndoManager(fragment, { trackedOrigins: new Set([origin]) })
+  doc.transact(() => {
+    const e = new Y.XmlElement('test')
+    e.setAttribute('a', '1')
+    e.setAttribute('b', '2')
+    fragment.insert(0, [e])
+  })
+  t.compareStrings(fragment.toString(), '<test a="1" b="2"></test>')
+  doc.transact(() => {
+    // change attribute "b" and delete test-node
+    const e = fragment.get(0)
+    e.setAttribute('b', '3')
+    fragment.delete(0)
+  }, origin)
+  t.compareStrings(fragment.toString(), '')
+  undoManager.undo()
+  t.compareStrings(fragment.toString(), '<test a="1" b="2"></test>')
+}
+
+/**
+ * Deleted entries in a map should be restored on undo.
+ *
+ * @see https://github.com/yjs/yjs/issues/500
+ * @param {t.TestCase} tc
+ */
+export const testUndoDeleteInMap = (tc) => {
+  const { map0 } = init(tc, { users: 3 })
+  const undoManager = new Y.UndoManager(map0, { captureTimeout: 0 })
+  map0.set('a', 'a')
+  map0.delete('a')
+  map0.set('a', 'b')
+  map0.delete('a')
+  map0.set('a', 'c')
+  map0.delete('a')
+  map0.set('a', 'd')
+  t.compare(map0.toJSON(), { a: 'd' })
+  undoManager.undo()
+  t.compare(map0.toJSON(), {})
+  undoManager.undo()
+  t.compare(map0.toJSON(), { a: 'c' })
+  undoManager.undo()
+  t.compare(map0.toJSON(), {})
+  undoManager.undo()
+  t.compare(map0.toJSON(), { a: 'b' })
+  undoManager.undo()
+  t.compare(map0.toJSON(), {})
+  undoManager.undo()
+  t.compare(map0.toJSON(), { a: 'a' })
+}
+
+/**
+ * It should expose the StackItem being processed if undoing
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testUndoDoingStackItem = async (_tc) => {
+  const doc = new Y.Doc()
+  const text = doc.getText('text')
+  const undoManager = new Y.UndoManager([text])
+  undoManager.on('stack-item-added', /** @param {any} event */ event => {
+    event.stackItem.meta.set('str', '42')
+  })
+  let metaUndo = /** @type {any} */ (null)
+  let metaRedo = /** @type {any} */ (null)
+  text.observe((event) => {
+    const /** @type {Y.UndoManager} */ origin = event.transaction.origin
+    if (origin === undoManager && origin.undoing) {
+      metaUndo = origin.currStackItem?.meta.get('str')
+    } else if (origin === undoManager && origin.redoing) {
+      metaRedo = origin.currStackItem?.meta.get('str')
+    }
+  })
+  text.insert(0, 'abc')
+  undoManager.undo()
+  undoManager.redo()
+  t.compare(metaUndo, '42', 'currStackItem is accessible while undoing')
+  t.compare(metaRedo, '42', 'currStackItem is accessible while redoing')
+  t.compare(undoManager.currStackItem, null, 'currStackItem is null after observe/transaction')
+}
--- a/tests/updates.tests.js
+++ b/tests/updates.tests.js
@ -0,0 +1,357 @@
+import * as t from 'lib0/testing'
+import { init, compare } from './testHelper.js' // eslint-disable-line
+import * as Y from '../src/index.js'
+import { readClientsStructRefs, readDeleteSet, UpdateDecoderV2, UpdateEncoderV2, writeDeleteSet } from '../src/internals.js'
+import * as encoding from 'lib0/encoding'
+import * as decoding from 'lib0/decoding'
+import * as object from 'lib0/object'
+
+/**
+ * @typedef {Object} Enc
+ * @property {function(Array<Uint8Array>):Uint8Array} Enc.mergeUpdates
+ * @property {function(Y.Doc):Uint8Array} Enc.encodeStateAsUpdate
+ * @property {function(Y.Doc, Uint8Array):void} Enc.applyUpdate
+ * @property {function(Uint8Array):void} Enc.logUpdate
+ * @property {function(Uint8Array):{from:Map<number,number>,to:Map<number,number>}} Enc.parseUpdateMeta
+ * @property {function(Y.Doc):Uint8Array} Enc.encodeStateVector
+ * @property {function(Uint8Array):Uint8Array} Enc.encodeStateVectorFromUpdate
+ * @property {'update'|'updateV2'} Enc.updateEventName
+ * @property {string} Enc.description
+ * @property {function(Uint8Array, Uint8Array):Uint8Array} Enc.diffUpdate
+ */
+
+/**
+ * @type {Enc}
+ */
+const encV1 = {
+  mergeUpdates: Y.mergeUpdates,
+  encodeStateAsUpdate: Y.encodeStateAsUpdate,
+  applyUpdate: Y.applyUpdate,
+  logUpdate: Y.logUpdate,
+  parseUpdateMeta: Y.parseUpdateMeta,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdate,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'update',
+  description: 'V1',
+  diffUpdate: Y.diffUpdate
+}
+
+/**
+ * @type {Enc}
+ */
+const encV2 = {
+  mergeUpdates: Y.mergeUpdatesV2,
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  parseUpdateMeta: Y.parseUpdateMetaV2,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdateV2,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'updateV2',
+  description: 'V2',
+  diffUpdate: Y.diffUpdateV2
+}
+
+/**
+ * @type {Enc}
+ */
+const encDoc = {
+  mergeUpdates: (updates) => {
+    const ydoc = new Y.Doc({ gc: false })
+    updates.forEach(update => {
+      Y.applyUpdateV2(ydoc, update)
+    })
+    return Y.encodeStateAsUpdateV2(ydoc)
+  },
+  encodeStateAsUpdate: Y.encodeStateAsUpdateV2,
+  applyUpdate: Y.applyUpdateV2,
+  logUpdate: Y.logUpdateV2,
+  parseUpdateMeta: Y.parseUpdateMetaV2,
+  encodeStateVectorFromUpdate: Y.encodeStateVectorFromUpdateV2,
+  encodeStateVector: Y.encodeStateVector,
+  updateEventName: 'updateV2',
+  description: 'Merge via Y.Doc',
+  /**
+   * @param {Uint8Array} update
+   * @param {Uint8Array} sv
+   */
+  diffUpdate: (update, sv) => {
+    const ydoc = new Y.Doc({ gc: false })
+    Y.applyUpdateV2(ydoc, update)
+    return Y.encodeStateAsUpdateV2(ydoc, sv)
+  }
+}
+
+const encoders = [encV1, encV2, encDoc]
+
+/**
+ * @param {Array<Y.Doc>} users
+ * @param {Enc} enc
+ */
+const fromUpdates = (users, enc) => {
+  const updates = users.map(user =>
+    enc.encodeStateAsUpdate(user)
+  )
+  const ydoc = new Y.Doc()
+  enc.applyUpdate(ydoc, enc.mergeUpdates(updates))
+  return ydoc
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergeUpdates = tc => {
+  const { users, array0, array1 } = init(tc, { users: 3 })
+
+  array0.insert(0, [1])
+  array1.insert(0, [2])
+
+  compare(users)
+  encoders.forEach(enc => {
+    const merged = fromUpdates(users, enc)
+    t.compareArrays(array0.toArray(), merged.getArray('array').toArray())
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testKeyEncoding = tc => {
+  const { users, text0, text1 } = init(tc, { users: 2 })
+
+  text0.insert(0, 'a', { italic: true })
+  text0.insert(0, 'b')
+  text0.insert(0, 'c', { italic: true })
+
+  const update = Y.encodeStateAsUpdateV2(users[0])
+  Y.applyUpdateV2(users[1], update)
+
+  t.compare(text1.toDelta(), [{ insert: 'c', attributes: { italic: true } }, { insert: 'b' }, { insert: 'a', attributes: { italic: true } }])
+
+  compare(users)
+}
+
+/**
+ * @param {Y.Doc} ydoc
+ * @param {Array<Uint8Array>} updates - expecting at least 4 updates
+ * @param {Enc} enc
+ * @param {boolean} hasDeletes
+ */
+const checkUpdateCases = (ydoc, updates, enc, hasDeletes) => {
+  const cases = []
+  // Case 1: Simple case, simply merge everything
+  cases.push(enc.mergeUpdates(updates))
+
+  // Case 2: Overlapping updates
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates(updates.slice(2)),
+    enc.mergeUpdates(updates.slice(0, 2))
+  ]))
+
+  // Case 3: Overlapping updates
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates(updates.slice(2)),
+    enc.mergeUpdates(updates.slice(1, 3)),
+    updates[0]
+  ]))
+
+  // Case 4: Separated updates (containing skips)
+  cases.push(enc.mergeUpdates([
+    enc.mergeUpdates([updates[0], updates[2]]),
+    enc.mergeUpdates([updates[1], updates[3]]),
+    enc.mergeUpdates(updates.slice(4))
+  ]))
+
+  // Case 5: overlapping with many duplicates
+  cases.push(enc.mergeUpdates(cases))
+
+  // const targetState = enc.encodeStateAsUpdate(ydoc)
+  // t.info('Target State: ')
+  // enc.logUpdate(targetState)
+
+  cases.forEach((mergedUpdates) => {
+    // t.info('State Case $' + i + ':')
+    // enc.logUpdate(updates)
+    const merged = new Y.Doc({ gc: false })
+    enc.applyUpdate(merged, mergedUpdates)
+    t.compareArrays(merged.getArray().toArray(), ydoc.getArray().toArray())
+    t.compare(enc.encodeStateVector(merged), enc.encodeStateVectorFromUpdate(mergedUpdates))
+
+    if (enc.updateEventName !== 'update') { // @todo should this also work on legacy updates?
+      for (let j = 1; j < updates.length; j++) {
+        const partMerged = enc.mergeUpdates(updates.slice(j))
+        const partMeta = enc.parseUpdateMeta(partMerged)
+        const targetSV = Y.encodeStateVectorFromUpdateV2(Y.mergeUpdatesV2(updates.slice(0, j)))
+        const diffed = enc.diffUpdate(mergedUpdates, targetSV)
+        const diffedMeta = enc.parseUpdateMeta(diffed)
+        t.compare(partMeta, diffedMeta)
+        {
+          // We can'd do the following
+          //  - t.compare(diffed, mergedDeletes)
+          // because diffed contains the set of all deletes.
+          // So we add all deletes from `diffed` to `partDeletes` and compare then
+          const decoder = decoding.createDecoder(diffed)
+          const updateDecoder = new UpdateDecoderV2(decoder)
+          readClientsStructRefs(updateDecoder, new Y.Doc())
+          const ds = readDeleteSet(updateDecoder)
+          const updateEncoder = new UpdateEncoderV2()
+          encoding.writeVarUint(updateEncoder.restEncoder, 0) // 0 structs
+          writeDeleteSet(updateEncoder, ds)
+          const deletesUpdate = updateEncoder.toUint8Array()
+          const mergedDeletes = Y.mergeUpdatesV2([deletesUpdate, partMerged])
+          if (!hasDeletes || enc !== encDoc) {
+            // deletes will almost definitely lead to different encoders because of the mergeStruct feature that is present in encDoc
+            t.compare(diffed, mergedDeletes)
+          }
+        }
+      }
+    }
+
+    const meta = enc.parseUpdateMeta(mergedUpdates)
+    meta.from.forEach((clock, client) => t.assert(clock === 0))
+    meta.to.forEach((clock, client) => {
+      const structs = /** @type {Array<Y.Item>} */ (merged.store.clients.get(client))
+      const lastStruct = structs[structs.length - 1]
+      t.assert(lastStruct.id.clock + lastStruct.length === clock)
+    })
+  })
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testMergeUpdates1 = _tc => {
+  encoders.forEach((enc) => {
+    t.info(`Using encoder: ${enc.description}`)
+    const ydoc = new Y.Doc({ gc: false })
+    const updates = /** @type {Array<Uint8Array>} */ ([])
+    ydoc.on(enc.updateEventName, update => { updates.push(update) })
+
+    const array = ydoc.getArray()
+    array.insert(0, [1])
+    array.insert(0, [2])
+    array.insert(0, [3])
+    array.insert(0, [4])
+
+    checkUpdateCases(ydoc, updates, enc, false)
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergeUpdates2 = tc => {
+  encoders.forEach((enc, i) => {
+    t.info(`Using encoder: ${enc.description}`)
+    const ydoc = new Y.Doc({ gc: false })
+    const updates = /** @type {Array<Uint8Array>} */ ([])
+    ydoc.on(enc.updateEventName, update => { updates.push(update) })
+
+    const array = ydoc.getArray()
+    array.insert(0, [1, 2])
+    array.delete(1, 1)
+    array.insert(0, [3, 4])
+    array.delete(1, 2)
+
+    checkUpdateCases(ydoc, updates, enc, true)
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMergePendingUpdates = tc => {
+  const yDoc = new Y.Doc()
+  /**
+   * @type {Array<Uint8Array>}
+   */
+  const serverUpdates = []
+  yDoc.on('update', (update, origin, c) => {
+    serverUpdates.splice(serverUpdates.length, 0, update)
+  })
+  const yText = yDoc.getText('textBlock')
+  yText.applyDelta([{ insert: 'r' }])
+  yText.applyDelta([{ insert: 'o' }])
+  yText.applyDelta([{ insert: 'n' }])
+  yText.applyDelta([{ insert: 'e' }])
+  yText.applyDelta([{ insert: 'n' }])
+
+  const yDoc1 = new Y.Doc()
+  Y.applyUpdate(yDoc1, serverUpdates[0])
+  const update1 = Y.encodeStateAsUpdate(yDoc1)
+
+  const yDoc2 = new Y.Doc()
+  Y.applyUpdate(yDoc2, update1)
+  Y.applyUpdate(yDoc2, serverUpdates[1])
+  const update2 = Y.encodeStateAsUpdate(yDoc2)
+
+  const yDoc3 = new Y.Doc()
+  Y.applyUpdate(yDoc3, update2)
+  Y.applyUpdate(yDoc3, serverUpdates[3])
+  const update3 = Y.encodeStateAsUpdate(yDoc3)
+
+  const yDoc4 = new Y.Doc()
+  Y.applyUpdate(yDoc4, update3)
+  Y.applyUpdate(yDoc4, serverUpdates[2])
+  const update4 = Y.encodeStateAsUpdate(yDoc4)
+
+  const yDoc5 = new Y.Doc()
+  Y.applyUpdate(yDoc5, update4)
+  Y.applyUpdate(yDoc5, serverUpdates[4])
+  // @ts-ignore
+  const _update5 = Y.encodeStateAsUpdate(yDoc5) // eslint-disable-line
+
+  const yText5 = yDoc5.getText('textBlock')
+  t.compareStrings(yText5.toString(), 'nenor')
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testObfuscateUpdates = _tc => {
+  const ydoc = new Y.Doc()
+  const ytext = ydoc.getText('text')
+  const ymap = ydoc.getMap('map')
+  const yarray = ydoc.getArray('array')
+  // test ytext
+  ytext.applyDelta([{ insert: 'text', attributes: { bold: true } }, { insert: { href: 'supersecreturl' } }])
+  // test ymap
+  ymap.set('key', 'secret1')
+  ymap.set('key', 'secret2')
+  // test yarray with subtype & subdoc
+  const subtype = new Y.XmlElement('secretnodename')
+  const subdoc = new Y.Doc({ guid: 'secret' })
+  subtype.setAttribute('attr', 'val')
+  yarray.insert(0, ['teststring', 42, subtype, subdoc])
+  // obfuscate the content and put it into a new document
+  const obfuscatedUpdate = Y.obfuscateUpdate(Y.encodeStateAsUpdate(ydoc))
+  const odoc = new Y.Doc()
+  Y.applyUpdate(odoc, obfuscatedUpdate)
+  const otext = odoc.getText('text')
+  const omap = odoc.getMap('map')
+  const oarray = odoc.getArray('array')
+  // test ytext
+  const delta = otext.toDelta()
+  t.assert(delta.length === 2)
+  t.assert(delta[0].insert !== 'text' && delta[0].insert.length === 4)
+  t.assert(object.length(delta[0].attributes) === 1)
+  t.assert(!object.hasProperty(delta[0].attributes, 'bold'))
+  t.assert(object.length(delta[1]) === 1)
+  t.assert(object.hasProperty(delta[1], 'insert'))
+  // test ymap
+  t.assert(omap.size === 1)
+  t.assert(!omap.has('key'))
+  // test yarray with subtype & subdoc
+  const result = oarray.toArray()
+  t.assert(result.length === 4)
+  t.assert(result[0] !== 'teststring')
+  t.assert(result[1] !== 42)
+  const osubtype = /** @type {Y.XmlElement} */ (result[2])
+  const osubdoc = result[3]
+  // test subtype
+  t.assert(osubtype.nodeName !== subtype.nodeName)
+  t.assert(object.length(osubtype.getAttributes()) === 1)
+  t.assert(osubtype.getAttribute('attr') === undefined)
+  // test subdoc
+  t.assert(osubdoc.guid !== subdoc.guid)
+}
--- a/tests/y-array.tests.js
+++ b/tests/y-array.tests.js
@ -0,0 +1,691 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+import * as math from 'lib0/math'
+import * as env from 'lib0/environment'
+
+const isDevMode = env.getVariable('node_env') === 'development'
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicUpdate = tc => {
+  const doc1 = new Y.Doc()
+  const doc2 = new Y.Doc()
+  doc1.getArray('array').insert(0, ['hi'])
+  const update = Y.encodeStateAsUpdate(doc1)
+  Y.applyUpdate(doc2, update)
+  t.compare(doc2.getArray('array').toArray(), ['hi'])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testFailsObjectManipulationInDevMode = tc => {
+  if (isDevMode) {
+    t.info('running in dev mode')
+    const doc = new Y.Doc()
+    const a = [1, 2, 3]
+    const b = { o: 1 }
+    doc.getArray('test').insert(0, [a])
+    doc.getMap('map').set('k', b)
+    t.fails(() => {
+      a[0] = 42
+    })
+    t.fails(() => {
+      b.o = 42
+    })
+  } else {
+    t.info('not in dev mode')
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSlice = tc => {
+  const doc1 = new Y.Doc()
+  const arr = doc1.getArray('array')
+  arr.insert(0, [1, 2, 3])
+  t.compareArrays(arr.slice(0), [1, 2, 3])
+  t.compareArrays(arr.slice(1), [2, 3])
+  t.compareArrays(arr.slice(0, -1), [1, 2])
+  arr.insert(0, [0])
+  t.compareArrays(arr.slice(0), [0, 1, 2, 3])
+  t.compareArrays(arr.slice(0, 2), [0, 1])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testArrayFrom = tc => {
+  const doc1 = new Y.Doc()
+  const db1 = doc1.getMap('root')
+  const nestedArray1 = Y.Array.from([0, 1, 2])
+  db1.set('array', nestedArray1)
+  t.compare(nestedArray1.toArray(), [0, 1, 2])
+}
+
+/**
+ * Debugging yjs#297 - a critical bug connected to the search-marker approach
+ *
+ * @param {t.TestCase} tc
+ */
+export const testLengthIssue = tc => {
+  const doc1 = new Y.Doc()
+  const arr = doc1.getArray('array')
+  arr.push([0, 1, 2, 3])
+  arr.delete(0)
+  arr.insert(0, [0])
+  t.assert(arr.length === arr.toArray().length)
+  doc1.transact(() => {
+    arr.delete(1)
+    t.assert(arr.length === arr.toArray().length)
+    arr.insert(1, [1])
+    t.assert(arr.length === arr.toArray().length)
+    arr.delete(2)
+    t.assert(arr.length === arr.toArray().length)
+    arr.insert(2, [2])
+    t.assert(arr.length === arr.toArray().length)
+  })
+  t.assert(arr.length === arr.toArray().length)
+  arr.delete(1)
+  t.assert(arr.length === arr.toArray().length)
+  arr.insert(1, [1])
+  t.assert(arr.length === arr.toArray().length)
+}
+
+/**
+ * Debugging yjs#314
+ *
+ * @param {t.TestCase} tc
+ */
+export const testLengthIssue2 = tc => {
+  const doc = new Y.Doc()
+  const next = doc.getArray()
+  doc.transact(() => {
+    next.insert(0, ['group2'])
+  })
+  doc.transact(() => {
+    next.insert(1, ['rectangle3'])
+  })
+  doc.transact(() => {
+    next.delete(0)
+    next.insert(0, ['rectangle3'])
+  })
+  next.delete(1)
+  doc.transact(() => {
+    next.insert(1, ['ellipse4'])
+  })
+  doc.transact(() => {
+    next.insert(2, ['ellipse3'])
+  })
+  doc.transact(() => {
+    next.insert(3, ['ellipse2'])
+  })
+  doc.transact(() => {
+    doc.transact(() => {
+      t.fails(() => {
+        next.insert(5, ['rectangle2'])
+      })
+      next.insert(4, ['rectangle2'])
+    })
+    doc.transact(() => {
+      // this should not throw an error message
+      next.delete(4)
+    })
+  })
+  console.log(next.toArray())
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeleteInsert = tc => {
+  const { users, array0 } = init(tc, { users: 2 })
+  array0.delete(0, 0)
+  t.describe('Does not throw when deleting zero elements with position 0')
+  t.fails(() => {
+    array0.delete(1, 1)
+  })
+  array0.insert(0, ['A'])
+  array0.delete(1, 0)
+  t.describe('Does not throw when deleting zero elements with valid position 1')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertThreeElementsTryRegetProperty = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, [1, true, false])
+  t.compare(array0.toJSON(), [1, true, false], '.toJSON() works')
+  testConnector.flushAllMessages()
+  t.compare(array1.toJSON(), [1, true, false], '.toJSON() works after sync')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testConcurrentInsertWithThreeConflicts = tc => {
+  const { users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, [0])
+  array1.insert(0, [1])
+  array2.insert(0, [2])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testConcurrentInsertDeleteWithThreeConflicts = tc => {
+  const { testConnector, users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  array0.insert(1, [0])
+  array1.delete(0)
+  array1.delete(1, 1)
+  array2.insert(1, [2])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertionsInLateSync = tc => {
+  const { testConnector, users, array0, array1, array2 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  users[2].disconnect()
+  array0.insert(1, ['user0'])
+  array1.insert(1, ['user1'])
+  array2.insert(1, ['user2'])
+  users[1].connect()
+  users[2].connect()
+  testConnector.flushAllMessages()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDisconnectReallyPreventsSendingMessages = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  users[2].disconnect()
+  array0.insert(1, ['user0'])
+  array1.insert(1, ['user1'])
+  t.compare(array0.toJSON(), ['x', 'user0', 'y'])
+  t.compare(array1.toJSON(), ['x', 'user1', 'y'])
+  users[1].connect()
+  users[2].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testDeletionsInLateSync = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, ['x', 'y'])
+  testConnector.flushAllMessages()
+  users[1].disconnect()
+  array1.delete(1, 1)
+  array0.delete(0, 2)
+  users[1].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertThenMergeDeleteOnSync = tc => {
+  const { testConnector, users, array0, array1 } = init(tc, { users: 2 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  users[0].disconnect()
+  array1.delete(0, 3)
+  users[0].connect()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEvents = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>?}
+   */
+  let event = null
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, [0, 1, 2])
+  t.assert(event !== null)
+  event = null
+  array0.delete(0)
+  t.assert(event !== null)
+  event = null
+  array0.delete(0, 2)
+  t.assert(event !== null)
+  event = null
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testNestedObserverEvents = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<number>}
+   */
+  const vals = []
+  array0.observe(e => {
+    if (array0.length === 1) {
+      // inserting, will call this observer again
+      // we expect that this observer is called after this event handler finishedn
+      array0.insert(1, [1])
+      vals.push(0)
+    } else {
+      // this should be called the second time an element is inserted (above case)
+      vals.push(1)
+    }
+  })
+  array0.insert(0, [0])
+  t.compareArrays(vals, [0, 1])
+  t.compareArrays(array0.toArray(), [0, 1])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEventsForTypes = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>|null}
+   */
+  let event = null
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, [new Y.Array()])
+  t.assert(event !== null)
+  event = null
+  array0.delete(0)
+  t.assert(event !== null)
+  event = null
+  compare(users)
+}
+
+/**
+ * This issue has been reported in https://discuss.yjs.dev/t/order-in-which-events-yielded-by-observedeep-should-be-applied/261/2
+ *
+ * Deep observers generate multiple events. When an array added at item at, say, position 0,
+ * and item 1 changed then the array-add event should fire first so that the change event
+ * path is correct. A array binding might lead to an inconsistent state otherwise.
+ *
+ * @param {t.TestCase} tc
+ */
+export const testObserveDeepEventOrder = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<any>}
+   */
+  let events = []
+  array0.observeDeep(e => {
+    events = e
+  })
+  array0.insert(0, [new Y.Map()])
+  users[0].transact(() => {
+    array0.get(0).set('a', 'a')
+    array0.insert(0, [0])
+  })
+  for (let i = 1; i < events.length; i++) {
+    t.assert(events[i - 1].path.length <= events[i].path.length, 'path size increases, fire top-level events first')
+  }
+}
+
+/**
+ * Correct index when computing event.path in observeDeep - https://github.com/yjs/yjs/issues/457
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testObservedeepIndexes = _tc => {
+  const doc = new Y.Doc()
+  const map = doc.getMap()
+  // Create a field with the array as value
+  map.set('my-array', new Y.Array())
+  // Fill the array with some strings and our Map
+  map.get('my-array').push(['a', 'b', 'c', new Y.Map()])
+  /**
+   * @type {Array<any>}
+   */
+  let eventPath = []
+  map.observeDeep((events) => { eventPath = events[0].path })
+  // set a value on the map inside of our array
+  map.get('my-array').get(3).set('hello', 'world')
+  console.log(eventPath)
+  t.compare(eventPath, ['my-array', 3])
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testChangeEvent = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let changes = null
+  array0.observe(e => {
+    changes = e.changes
+  })
+  const newArr = new Y.Array()
+  array0.insert(0, [newArr, 4, 'dtrn'])
+  t.assert(changes !== null && changes.added.size === 2 && changes.deleted.size === 0)
+  t.compare(changes.delta, [{ insert: [newArr, 4, 'dtrn'] }])
+  changes = null
+  array0.delete(0, 2)
+  t.assert(changes !== null && changes.added.size === 0 && changes.deleted.size === 2)
+  t.compare(changes.delta, [{ delete: 2 }])
+  changes = null
+  array0.insert(1, [0.1])
+  t.assert(changes !== null && changes.added.size === 1 && changes.deleted.size === 0)
+  t.compare(changes.delta, [{ retain: 1 }, { insert: [0.1] }])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testInsertAndDeleteEventsForTypes2 = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  /**
+   * @type {Array<Object<string,any>>}
+   */
+  const events = []
+  array0.observe(e => {
+    events.push(e)
+  })
+  array0.insert(0, ['hi', new Y.Map()])
+  t.assert(events.length === 1, 'Event is triggered exactly once for insertion of two elements')
+  array0.delete(1)
+  t.assert(events.length === 2, 'Event is triggered exactly once for deletion')
+  compare(users)
+}
+
+/**
+ * This issue has been reported here https://github.com/yjs/yjs/issues/155
+ * @param {t.TestCase} tc
+ */
+export const testNewChildDoesNotEmitEventInTransaction = tc => {
+  const { array0, users } = init(tc, { users: 2 })
+  let fired = false
+  users[0].transact(() => {
+    const newMap = new Y.Map()
+    newMap.observe(() => {
+      fired = true
+    })
+    array0.insert(0, [newMap])
+    newMap.set('tst', 42)
+  })
+  t.assert(!fired, 'Event does not trigger')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGarbageCollector = tc => {
+  const { testConnector, users, array0 } = init(tc, { users: 3 })
+  array0.insert(0, ['x', 'y', 'z'])
+  testConnector.flushAllMessages()
+  users[0].disconnect()
+  array0.delete(0, 3)
+  users[0].connect()
+  testConnector.flushAllMessages()
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEventTargetIsSetCorrectlyOnLocal = tc => {
+  const { array0, users } = init(tc, { users: 3 })
+  /**
+   * @type {any}
+   */
+  let event
+  array0.observe(e => {
+    event = e
+  })
+  array0.insert(0, ['stuff'])
+  t.assert(event.target === array0, '"target" property is set correctly')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEventTargetIsSetCorrectlyOnRemote = tc => {
+  const { testConnector, array0, array1, users } = init(tc, { users: 3 })
+  /**
+   * @type {any}
+   */
+  let event
+  array0.observe(e => {
+    event = e
+  })
+  array1.insert(0, ['stuff'])
+  testConnector.flushAllMessages()
+  t.assert(event.target === array0, '"target" property is set correctly')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testIteratingArrayContainingTypes = tc => {
+  const y = new Y.Doc()
+  const arr = y.getArray('arr')
+  const numItems = 10
+  for (let i = 0; i < numItems; i++) {
+    const map = new Y.Map()
+    map.set('value', i)
+    arr.push([map])
+  }
+  let cnt = 0
+  for (const item of arr) {
+    t.assert(item.get('value') === cnt++, 'value is correct')
+  }
+  y.destroy()
+}
+
+let _uniqueNumber = 0
+const getUniqueNumber = () => _uniqueNumber++
+
+/**
+ * @type {Array<function(Doc,prng.PRNG,any):void>}
+ */
+const arrayTransactions = [
+  function insert (user, gen) {
+    const yarray = user.getArray('array')
+    const uniqueNumber = getUniqueNumber()
+    const content = []
+    const len = prng.int32(gen, 1, 4)
+    for (let i = 0; i < len; i++) {
+      content.push(uniqueNumber)
+    }
+    const pos = prng.int32(gen, 0, yarray.length)
+    const oldContent = yarray.toArray()
+    yarray.insert(pos, content)
+    oldContent.splice(pos, 0, ...content)
+    t.compareArrays(yarray.toArray(), oldContent) // we want to make sure that fastSearch markers insert at the correct position
+  },
+  function insertTypeArray (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Array()])
+    const array2 = yarray.get(pos)
+    array2.insert(0, [1, 2, 3, 4])
+  },
+  function insertTypeMap (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [new Y.Map()])
+    const map = yarray.get(pos)
+    map.set('someprop', 42)
+    map.set('someprop', 43)
+    map.set('someprop', 44)
+  },
+  function insertTypeNull (user, gen) {
+    const yarray = user.getArray('array')
+    const pos = prng.int32(gen, 0, yarray.length)
+    yarray.insert(pos, [null])
+  },
+  function _delete (user, gen) {
+    const yarray = user.getArray('array')
+    const length = yarray.length
+    if (length > 0) {
+      let somePos = prng.int32(gen, 0, length - 1)
+      let delLength = prng.int32(gen, 1, math.min(2, length - somePos))
+      if (prng.bool(gen)) {
+        const type = yarray.get(somePos)
+        if (type instanceof Y.Array && type.length > 0) {
+          somePos = prng.int32(gen, 0, type.length - 1)
+          delLength = prng.int32(gen, 0, math.min(2, type.length - somePos))
+          type.delete(somePos, delLength)
+        }
+      } else {
+        const oldContent = yarray.toArray()
+        yarray.delete(somePos, delLength)
+        oldContent.splice(somePos, delLength)
+        t.compareArrays(yarray.toArray(), oldContent)
+      }
+    }
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests6 = tc => {
+  applyRandomTests(tc, arrayTransactions, 6)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests40 = tc => {
+  applyRandomTests(tc, arrayTransactions, 40)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests42 = tc => {
+  applyRandomTests(tc, arrayTransactions, 42)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests43 = tc => {
+  applyRandomTests(tc, arrayTransactions, 43)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests44 = tc => {
+  applyRandomTests(tc, arrayTransactions, 44)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests45 = tc => {
+  applyRandomTests(tc, arrayTransactions, 45)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests46 = tc => {
+  applyRandomTests(tc, arrayTransactions, 46)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests300 = tc => {
+  applyRandomTests(tc, arrayTransactions, 300)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests400 = tc => {
+  applyRandomTests(tc, arrayTransactions, 400)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests500 = tc => {
+  applyRandomTests(tc, arrayTransactions, 500)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests600 = tc => {
+  applyRandomTests(tc, arrayTransactions, 600)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests1000 = tc => {
+  applyRandomTests(tc, arrayTransactions, 1000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests1800 = tc => {
+  applyRandomTests(tc, arrayTransactions, 1800)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests3000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 3000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests5000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 5000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYarrayTests30000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, arrayTransactions, 30000)
+}
--- a/tests/y-map.tests.js
+++ b/tests/y-map.tests.js
@ -0,0 +1,756 @@
+import { init, compare, applyRandomTests, Doc } from './testHelper.js' // eslint-disable-line
+
+import {
+  compareIDs
+} from '../src/internals.js'
+
+import * as Y from '../src/index.js'
+import * as t from 'lib0/testing'
+import * as prng from 'lib0/prng'
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testIterators = _tc => {
+  const ydoc = new Y.Doc()
+  /**
+   * @type {Y.Map<number>}
+   */
+  const ymap = ydoc.getMap()
+  // we are only checking if the type assumptions are correct
+  /**
+   * @type {Array<number>}
+   */
+  const vals = Array.from(ymap.values())
+  /**
+   * @type {Array<[string,number]>}
+   */
+  const entries = Array.from(ymap.entries())
+  /**
+   * @type {Array<string>}
+   */
+  const keys = Array.from(ymap.keys())
+  console.log(vals, entries, keys)
+}
+
+/**
+ * Computing event changes after transaction should result in an error. See yjs#539
+ *
+ * @param {t.TestCase} _tc
+ */
+export const testMapEventError = _tc => {
+  const doc = new Y.Doc()
+  const ymap = doc.getMap()
+  /**
+   * @type {any}
+   */
+  let event = null
+  ymap.observe((e) => {
+    event = e
+  })
+  t.fails(() => {
+    t.info(event.keys)
+  })
+  t.fails(() => {
+    t.info(event.keys)
+  })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testMapHavingIterableAsConstructorParamTests = tc => {
+  const { map0 } = init(tc, { users: 1 })
+
+  const m1 = new Y.Map(Object.entries({ number: 1, string: 'hello' }))
+  map0.set('m1', m1)
+  t.assert(m1.get('number') === 1)
+  t.assert(m1.get('string') === 'hello')
+
+  const m2 = new Y.Map([
+    ['object', { x: 1 }],
+    ['boolean', true]
+  ])
+  map0.set('m2', m2)
+  t.assert(m2.get('object').x === 1)
+  t.assert(m2.get('boolean') === true)
+
+  const m3 = new Y.Map([...m1, ...m2])
+  map0.set('m3', m3)
+  t.assert(m3.get('number') === 1)
+  t.assert(m3.get('string') === 'hello')
+  t.assert(m3.get('object').x === 1)
+  t.assert(m3.get('boolean') === true)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testBasicMapTests = tc => {
+  const { testConnector, users, map0, map1, map2 } = init(tc, { users: 3 })
+  users[2].disconnect()
+
+  map0.set('null', null)
+  map0.set('number', 1)
+  map0.set('string', 'hello Y')
+  map0.set('object', { key: { key2: 'value' } })
+  map0.set('y-map', new Y.Map())
+  map0.set('boolean1', true)
+  map0.set('boolean0', false)
+  const map = map0.get('y-map')
+  map.set('y-array', new Y.Array())
+  const array = map.get('y-array')
+  array.insert(0, [0])
+  array.insert(0, [-1])
+
+  t.assert(map0.get('null') === null, 'client 0 computed the change (null)')
+  t.assert(map0.get('number') === 1, 'client 0 computed the change (number)')
+  t.assert(map0.get('string') === 'hello Y', 'client 0 computed the change (string)')
+  t.assert(map0.get('boolean0') === false, 'client 0 computed the change (boolean)')
+  t.assert(map0.get('boolean1') === true, 'client 0 computed the change (boolean)')
+  t.compare(map0.get('object'), { key: { key2: 'value' } }, 'client 0 computed the change (object)')
+  t.assert(map0.get('y-map').get('y-array').get(0) === -1, 'client 0 computed the change (type)')
+  t.assert(map0.size === 7, 'client 0 map has correct size')
+
+  users[2].connect()
+  testConnector.flushAllMessages()
+
+  t.assert(map1.get('null') === null, 'client 1 received the update (null)')
+  t.assert(map1.get('number') === 1, 'client 1 received the update (number)')
+  t.assert(map1.get('string') === 'hello Y', 'client 1 received the update (string)')
+  t.assert(map1.get('boolean0') === false, 'client 1 computed the change (boolean)')
+  t.assert(map1.get('boolean1') === true, 'client 1 computed the change (boolean)')
+  t.compare(map1.get('object'), { key: { key2: 'value' } }, 'client 1 received the update (object)')
+  t.assert(map1.get('y-map').get('y-array').get(0) === -1, 'client 1 received the update (type)')
+  t.assert(map1.size === 7, 'client 1 map has correct size')
+
+  // compare disconnected user
+  t.assert(map2.get('null') === null, 'client 2 received the update (null) - was disconnected')
+  t.assert(map2.get('number') === 1, 'client 2 received the update (number) - was disconnected')
+  t.assert(map2.get('string') === 'hello Y', 'client 2 received the update (string) - was disconnected')
+  t.assert(map2.get('boolean0') === false, 'client 2 computed the change (boolean)')
+  t.assert(map2.get('boolean1') === true, 'client 2 computed the change (boolean)')
+  t.compare(map2.get('object'), { key: { key2: 'value' } }, 'client 2 received the update (object) - was disconnected')
+  t.assert(map2.get('y-map').get('y-array').get(0) === -1, 'client 2 received the update (type) - was disconnected')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapProperty = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 2 })
+  map0.set('stuff', 'stuffy')
+  map0.set('undefined', undefined)
+  map0.set('null', null)
+  t.compare(map0.get('stuff'), 'stuffy')
+
+  testConnector.flushAllMessages()
+
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'stuffy')
+    t.assert(u.get('undefined') === undefined, 'undefined')
+    t.compare(u.get('null'), null, 'null')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapSetsYmap = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  const map = map0.set('Map', new Y.Map())
+  t.assert(map0.get('Map') === map)
+  map.set('one', 1)
+  t.compare(map.get('one'), 1)
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapSetsYarray = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  const array = map0.set('Array', new Y.Array())
+  t.assert(array === map0.get('Array'))
+  array.insert(0, [1, 2, 3])
+  // @ts-ignore
+  t.compare(map0.toJSON(), { Array: [1, 2, 3] })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertySyncs = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 2 })
+  map0.set('stuff', 'stuffy')
+  t.compare(map0.get('stuff'), 'stuffy')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'stuffy')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertyWithConflict = tc => {
+  const { testConnector, users, map0, map1 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'c1')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSizeAndDeleteOfMapProperty = tc => {
+  const { map0 } = init(tc, { users: 1 })
+  map0.set('stuff', 'c0')
+  map0.set('otherstuff', 'c1')
+  t.assert(map0.size === 2, `map size is ${map0.size} expected 2`)
+  map0.delete('stuff')
+  t.assert(map0.size === 1, `map size after delete is ${map0.size}, expected 1`)
+  map0.delete('otherstuff')
+  t.assert(map0.size === 0, `map size after delete is ${map0.size}, expected 0`)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetAndDeleteOfMapProperty = tc => {
+  const { testConnector, users, map0, map1 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.delete('stuff')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetAndClearOfMapProperties = tc => {
+  const { testConnector, users, map0 } = init(tc, { users: 1 })
+  map0.set('stuff', 'c0')
+  map0.set('otherstuff', 'c1')
+  map0.clear()
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+    t.assert(u.get('otherstuff') === undefined)
+    t.assert(u.size === 0, `map size after clear is ${u.size}, expected 0`)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetAndClearOfMapPropertiesWithConflicts = tc => {
+  const { testConnector, users, map0, map1, map2, map3 } = init(tc, { users: 4 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  map0.set('otherstuff', 'c0')
+  map1.set('otherstuff', 'c1')
+  map2.set('otherstuff', 'c2')
+  map3.set('otherstuff', 'c3')
+  map3.clear()
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+    t.assert(u.get('otherstuff') === undefined)
+    t.assert(u.size === 0, `map size after clear is ${u.size}, expected 0`)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetOfMapPropertyWithThreeConflicts = tc => {
+  const { testConnector, users, map0, map1, map2 } = init(tc, { users: 3 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.compare(u.get('stuff'), 'c3')
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testGetAndSetAndDeleteOfMapPropertyWithThreeConflicts = tc => {
+  const { testConnector, users, map0, map1, map2, map3 } = init(tc, { users: 4 })
+  map0.set('stuff', 'c0')
+  map1.set('stuff', 'c1')
+  map1.set('stuff', 'c2')
+  map2.set('stuff', 'c3')
+  testConnector.flushAllMessages()
+  map0.set('stuff', 'deleteme')
+  map1.set('stuff', 'c1')
+  map2.set('stuff', 'c2')
+  map3.set('stuff', 'c3')
+  map3.delete('stuff')
+  testConnector.flushAllMessages()
+  for (const user of users) {
+    const u = user.getMap('map')
+    t.assert(u.get('stuff') === undefined)
+  }
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testObserveDeepProperties = tc => {
+  const { testConnector, users, map1, map2, map3 } = init(tc, { users: 4 })
+  const _map1 = map1.set('map', new Y.Map())
+  let calls = 0
+  let dmapid
+  map1.observeDeep(events => {
+    events.forEach(event => {
+      calls++
+      // @ts-ignore
+      t.assert(event.keysChanged.has('deepmap'))
+      t.assert(event.path.length === 1)
+      t.assert(event.path[0] === 'map')
+      // @ts-ignore
+      dmapid = event.target.get('deepmap')._item.id
+    })
+  })
+  testConnector.flushAllMessages()
+  const _map3 = map3.get('map')
+  _map3.set('deepmap', new Y.Map())
+  testConnector.flushAllMessages()
+  const _map2 = map2.get('map')
+  _map2.set('deepmap', new Y.Map())
+  testConnector.flushAllMessages()
+  const dmap1 = _map1.get('deepmap')
+  const dmap2 = _map2.get('deepmap')
+  const dmap3 = _map3.get('deepmap')
+  t.assert(calls > 0)
+  t.assert(compareIDs(dmap1._item.id, dmap2._item.id))
+  t.assert(compareIDs(dmap1._item.id, dmap3._item.id))
+  // @ts-ignore we want the possibility of dmapid being undefined
+  t.assert(compareIDs(dmap1._item.id, dmapid))
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testObserversUsingObservedeep = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Array<Array<string|number>>}
+   */
+  const paths = []
+  let calls = 0
+  map0.observeDeep(events => {
+    events.forEach(event => {
+      paths.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(paths, [[], ['map'], ['map', 'array']])
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testPathsOfSiblingEvents = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Array<Array<string|number>>}
+   */
+  const paths = []
+  let calls = 0
+  const doc = users[0]
+  map0.set('map', new Y.Map())
+  map0.get('map').set('text1', new Y.Text('initial'))
+  map0.observeDeep(events => {
+    events.forEach(event => {
+      paths.push(event.path)
+    })
+    calls++
+  })
+  doc.transact(() => {
+    map0.get('map').get('text1').insert(0, 'post-')
+    map0.get('map').set('text2', new Y.Text('new'))
+  })
+  t.assert(calls === 1)
+  t.compare(paths, [['map'], ['map', 'text1']])
+  compare(users)
+}
+
+// TODO: Test events in Y.Map
+/**
+ * @param {Object<string,any>} is
+ * @param {Object<string,any>} should
+ */
+const compareEvent = (is, should) => {
+  for (const key in should) {
+    t.compare(should[key], is[key])
+  }
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testThrowsAddAndUpdateAndDeleteEvents = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e // just put it on event, should be thrown synchronously anyway
+  })
+  map0.set('stuff', 4)
+  compareEvent(event, {
+    target: map0,
+    keysChanged: new Set(['stuff'])
+  })
+  // update, oldValue is in contents
+  map0.set('stuff', new Y.Array())
+  compareEvent(event, {
+    target: map0,
+    keysChanged: new Set(['stuff'])
+  })
+  // update, oldValue is in opContents
+  map0.set('stuff', 5)
+  // delete
+  map0.delete('stuff')
+  compareEvent(event, {
+    keysChanged: new Set(['stuff']),
+    target: map0
+  })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testThrowsDeleteEventsOnClear = tc => {
+  const { users, map0 } = init(tc, { users: 2 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e // just put it on event, should be thrown synchronously anyway
+  })
+  // set values
+  map0.set('stuff', 4)
+  map0.set('otherstuff', new Y.Array())
+  // clear
+  map0.clear()
+  compareEvent(event, {
+    keysChanged: new Set(['stuff', 'otherstuff']),
+    target: map0
+  })
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testChangeEvent = tc => {
+  const { map0, users } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let changes = null
+  /**
+   * @type {any}
+   */
+  let keyChange = null
+  map0.observe(e => {
+    changes = e.changes
+  })
+  map0.set('a', 1)
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  map0.set('a', 2)
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'update' && keyChange.oldValue === 1)
+  users[0].transact(() => {
+    map0.set('a', 3)
+    map0.set('a', 4)
+  })
+  keyChange = changes.keys.get('a')
+  t.assert(changes !== null && keyChange.action === 'update' && keyChange.oldValue === 2)
+  users[0].transact(() => {
+    map0.set('b', 1)
+    map0.set('b', 2)
+  })
+  keyChange = changes.keys.get('b')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  users[0].transact(() => {
+    map0.set('c', 1)
+    map0.delete('c')
+  })
+  t.assert(changes !== null && changes.keys.size === 0)
+  users[0].transact(() => {
+    map0.set('d', 1)
+    map0.set('d', 2)
+  })
+  keyChange = changes.keys.get('d')
+  t.assert(changes !== null && keyChange.action === 'add' && keyChange.oldValue === undefined)
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testYmapEventExceptionsShouldCompleteTransaction = _tc => {
+  const doc = new Y.Doc()
+  const map = doc.getMap('map')
+
+  let updateCalled = false
+  let throwingObserverCalled = false
+  let throwingDeepObserverCalled = false
+  doc.on('update', () => {
+    updateCalled = true
+  })
+
+  const throwingObserver = () => {
+    throwingObserverCalled = true
+    throw new Error('Failure')
+  }
+
+  const throwingDeepObserver = () => {
+    throwingDeepObserverCalled = true
+    throw new Error('Failure')
+  }
+
+  map.observe(throwingObserver)
+  map.observeDeep(throwingDeepObserver)
+
+  t.fails(() => {
+    map.set('y', '2')
+  })
+
+  t.assert(updateCalled)
+  t.assert(throwingObserverCalled)
+  t.assert(throwingDeepObserverCalled)
+
+  // check if it works again
+  updateCalled = false
+  throwingObserverCalled = false
+  throwingDeepObserverCalled = false
+  t.fails(() => {
+    map.set('z', '3')
+  })
+
+  t.assert(updateCalled)
+  t.assert(throwingObserverCalled)
+  t.assert(throwingDeepObserverCalled)
+
+  t.assert(map.get('z') === '3')
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapEventHasCorrectValueWhenSettingAPrimitive = tc => {
+  const { users, map0 } = init(tc, { users: 3 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e
+  })
+  map0.set('stuff', 2)
+  t.compare(event.value, event.target.get(event.name))
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testYmapEventHasCorrectValueWhenSettingAPrimitiveFromOtherUser = tc => {
+  const { users, map0, map1, testConnector } = init(tc, { users: 3 })
+  /**
+   * @type {Object<string,any>}
+   */
+  let event = {}
+  map0.observe(e => {
+    event = e
+  })
+  map1.set('stuff', 2)
+  testConnector.flushAllMessages()
+  t.compare(event.value, event.target.get(event.name))
+  compare(users)
+}
+
+/**
+ * @type {Array<function(Doc,prng.PRNG):void>}
+ */
+const mapTransactions = [
+  function set (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    const value = prng.utf16String(gen)
+    user.getMap('map').set(key, value)
+  },
+  function setType (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    const type = prng.oneOf(gen, [new Y.Array(), new Y.Map()])
+    user.getMap('map').set(key, type)
+    if (type instanceof Y.Array) {
+      type.insert(0, [1, 2, 3, 4])
+    } else {
+      type.set('deepkey', 'deepvalue')
+    }
+  },
+  function _delete (user, gen) {
+    const key = prng.oneOf(gen, ['one', 'two'])
+    user.getMap('map').delete(key)
+  }
+]
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests10 = tc => {
+  applyRandomTests(tc, mapTransactions, 3)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests40 = tc => {
+  applyRandomTests(tc, mapTransactions, 40)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests42 = tc => {
+  applyRandomTests(tc, mapTransactions, 42)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests43 = tc => {
+  applyRandomTests(tc, mapTransactions, 43)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests44 = tc => {
+  applyRandomTests(tc, mapTransactions, 44)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests45 = tc => {
+  applyRandomTests(tc, mapTransactions, 45)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests46 = tc => {
+  applyRandomTests(tc, mapTransactions, 46)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests300 = tc => {
+  applyRandomTests(tc, mapTransactions, 300)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests400 = tc => {
+  applyRandomTests(tc, mapTransactions, 400)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests500 = tc => {
+  applyRandomTests(tc, mapTransactions, 500)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests600 = tc => {
+  applyRandomTests(tc, mapTransactions, 600)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests1000 = tc => {
+  applyRandomTests(tc, mapTransactions, 1000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests1800 = tc => {
+  applyRandomTests(tc, mapTransactions, 1800)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests5000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 5000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests10000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 10000)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testRepeatGeneratingYmapTests100000 = tc => {
+  t.skip(!t.production)
+  applyRandomTests(tc, mapTransactions, 100000)
+}
--- a/tests/y-text.tests.js
+++ b/tests/y-text.tests.js
--- a/tests/y-xml.tests.js
+++ b/tests/y-xml.tests.js
@ -0,0 +1,223 @@
+import { init, compare } from './testHelper.js'
+import * as Y from '../src/index.js'
+
+import * as t from 'lib0/testing'
+
+export const testCustomTypings = () => {
+  const ydoc = new Y.Doc()
+  const ymap = ydoc.getMap()
+  /**
+   * @type {Y.XmlElement<{ num: number, str: string, [k:string]: object|number|string }>}
+   */
+  const yxml = ymap.set('yxml', new Y.XmlElement('test'))
+  /**
+   * @type {number|undefined}
+   */
+  const num = yxml.getAttribute('num')
+  /**
+   * @type {string|undefined}
+   */
+  const str = yxml.getAttribute('str')
+  /**
+   * @type {object|number|string|undefined}
+   */
+  const dtrn = yxml.getAttribute('dtrn')
+  const attrs = yxml.getAttributes()
+  /**
+   * @type {object|number|string|undefined}
+   */
+  const any = attrs.shouldBeAny
+  console.log({ num, str, dtrn, attrs, any })
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testSetProperty = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  xml0.setAttribute('height', '10')
+  t.assert(xml0.getAttribute('height') === '10', 'Simple set+get works')
+  testConnector.flushAllMessages()
+  t.assert(xml1.getAttribute('height') === '10', 'Simple set+get works (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testHasProperty = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  xml0.setAttribute('height', '10')
+  t.assert(xml0.hasAttribute('height'), 'Simple set+has works')
+  testConnector.flushAllMessages()
+  t.assert(xml1.hasAttribute('height'), 'Simple set+has works (remote)')
+
+  xml0.removeAttribute('height')
+  t.assert(!xml0.hasAttribute('height'), 'Simple set+remove+has works')
+  testConnector.flushAllMessages()
+  t.assert(!xml1.hasAttribute('height'), 'Simple set+remove+has works (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testEvents = tc => {
+  const { testConnector, users, xml0, xml1 } = init(tc, { users: 2 })
+  /**
+   * @type {any}
+   */
+  let event
+  /**
+   * @type {any}
+   */
+  let remoteEvent
+  xml0.observe(e => {
+    event = e
+  })
+  xml1.observe(e => {
+    remoteEvent = e
+  })
+  xml0.setAttribute('key', 'value')
+  t.assert(event.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on updated key')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on updated key (remote)')
+  // check attributeRemoved
+  xml0.removeAttribute('key')
+  t.assert(event.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on removed attribute')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.attributesChanged.has('key'), 'YXmlEvent.attributesChanged on removed attribute (remote)')
+  xml0.insert(0, [new Y.XmlText('some text')])
+  t.assert(event.childListChanged, 'YXmlEvent.childListChanged on inserted element')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.childListChanged, 'YXmlEvent.childListChanged on inserted element (remote)')
+  // test childRemoved
+  xml0.delete(0)
+  t.assert(event.childListChanged, 'YXmlEvent.childListChanged on deleted element')
+  testConnector.flushAllMessages()
+  t.assert(remoteEvent.childListChanged, 'YXmlEvent.childListChanged on deleted element (remote)')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} tc
+ */
+export const testTreewalker = tc => {
+  const { users, xml0 } = init(tc, { users: 3 })
+  const paragraph1 = new Y.XmlElement('p')
+  const paragraph2 = new Y.XmlElement('p')
+  const text1 = new Y.XmlText('init')
+  const text2 = new Y.XmlText('text')
+  paragraph1.insert(0, [text1, text2])
+  xml0.insert(0, [paragraph1, paragraph2, new Y.XmlElement('img')])
+  const allParagraphs = xml0.querySelectorAll('p')
+  t.assert(allParagraphs.length === 2, 'found exactly two paragraphs')
+  t.assert(allParagraphs[0] === paragraph1, 'querySelectorAll found paragraph1')
+  t.assert(allParagraphs[1] === paragraph2, 'querySelectorAll found paragraph2')
+  t.assert(xml0.querySelector('p') === paragraph1, 'querySelector found paragraph1')
+  compare(users)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testYtextAttributes = _tc => {
+  const ydoc = new Y.Doc()
+  const ytext = /** @type {Y.XmlText} */ (ydoc.get('', Y.XmlText))
+  ytext.observe(event => {
+    t.compare(event.changes.keys.get('test'), { action: 'add', oldValue: undefined })
+  })
+  ytext.setAttribute('test', 42)
+  t.compare(ytext.getAttribute('test'), 42)
+  t.compare(ytext.getAttributes(), { test: 42 })
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testSiblings = _tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText()
+  const second = new Y.XmlElement('p')
+  yxml.insert(0, [first, second])
+  t.assert(first.nextSibling === second)
+  t.assert(second.prevSibling === first)
+  t.assert(first.parent === yxml)
+  t.assert(yxml.parent === null)
+  t.assert(yxml.firstChild === first)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testInsertafter = _tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText()
+  const second = new Y.XmlElement('p')
+  const third = new Y.XmlElement('p')
+
+  const deepsecond1 = new Y.XmlElement('span')
+  const deepsecond2 = new Y.XmlText()
+  second.insertAfter(null, [deepsecond1])
+  second.insertAfter(deepsecond1, [deepsecond2])
+
+  yxml.insertAfter(null, [first, second])
+  yxml.insertAfter(second, [third])
+
+  t.assert(yxml.length === 3)
+  t.assert(second.get(0) === deepsecond1)
+  t.assert(second.get(1) === deepsecond2)
+
+  t.compareArrays(yxml.toArray(), [first, second, third])
+
+  t.fails(() => {
+    const el = new Y.XmlElement('p')
+    el.insertAfter(deepsecond1, [new Y.XmlText()])
+  })
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testClone = _tc => {
+  const ydoc = new Y.Doc()
+  const yxml = ydoc.getXmlFragment()
+  const first = new Y.XmlText('text')
+  const second = new Y.XmlElement('p')
+  const third = new Y.XmlElement('p')
+  yxml.push([first, second, third])
+  t.compareArrays(yxml.toArray(), [first, second, third])
+  const cloneYxml = yxml.clone()
+  ydoc.getArray('copyarr').insert(0, [cloneYxml])
+  t.assert(cloneYxml.length === 3)
+  t.compare(cloneYxml.toJSON(), yxml.toJSON())
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testFormattingBug = _tc => {
+  const ydoc = new Y.Doc()
+  const yxml = /** @type {Y.XmlText} */ (ydoc.get('', Y.XmlText))
+  const delta = [
+    { insert: 'A', attributes: { em: {}, strong: {} } },
+    { insert: 'B', attributes: { em: {} } },
+    { insert: 'C', attributes: { em: {}, strong: {} } }
+  ]
+  yxml.applyDelta(delta)
+  t.compare(yxml.toDelta(), delta)
+}
+
+/**
+ * @param {t.TestCase} _tc
+ */
+export const testElement = _tc => {
+  const ydoc = new Y.Doc()
+  const yxmlel = ydoc.getXmlElement()
+  const text1 = new Y.XmlText('text1')
+  const text2 = new Y.XmlText('text2')
+  yxmlel.insert(0, [text1, text2])
+  t.compareArrays(yxmlel.toArray(), [text1, text2])
+}
--- a/tsconfig.json
+++ b/tsconfig.json
@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "ES2021",
+    "lib": ["ES2021", "dom"],
+    "module": "node16",
+    "allowJs": true,
+    "checkJs": true,
+    "declaration": true,
+    "declarationMap": true,
+    "outDir": "./dist",
+    "baseUrl": "./",
+    "emitDeclarationOnly": true,
+    "strict": true,
+    "noImplicitAny": true,
+    "moduleResolution": "nodenext",
+    "paths": {
+      "yjs": ["./src/index.js"]
+    }
+  },
+  "include": ["./src/**/*.js", "./tests/**/*.js"]
+}
--- a/y.es6
+++ b/y.es6
--- a/y.es6.map
+++ b/y.es6.map
--- a/y.js
+++ b/y.js
--- a/y.js.map
+++ b/y.js.map