diff --git a/jupyter_collaboration/app.py b/jupyter_collaboration/app.py
index 2c35982e..e36f513b 100644
--- a/jupyter_collaboration/app.py
+++ b/jupyter_collaboration/app.py
@@ -8,7 +8,7 @@
 from pycrdt_websocket.ystore import BaseYStore
 from traitlets import Bool, Float, Type
 
-from .handlers import DocSessionHandler, YDocWebSocketHandler
+from .handlers import DocForkHandler, DocDeleteHandler, DocMergeHandler, DocSessionHandler, YDocWebSocketHandler
 from .loaders import FileLoaderMapping
 from .stores import SQLiteYStore
 from .utils import AWARENESS_EVENTS_SCHEMA_PATH, EVENTS_SCHEMA_PATH
@@ -109,6 +109,27 @@ def initialize_handlers(self):
                     },
                 ),
                 (r"/api/collaboration/session/(.*)", DocSessionHandler),
+                (
+                    r"/api/collaboration/fork_room/(.*)",
+                    DocForkHandler,
+                    {
+                        "ywebsocket_server": self.ywebsocket_server,
+                    }
+                ),
+                (
+                    r"/api/collaboration/merge_room",
+                    DocMergeHandler,
+                    {
+                        "ywebsocket_server": self.ywebsocket_server,
+                    }
+                ),
+                (
+                    r"/api/collaboration/delete_room",
+                    DocDeleteHandler,
+                    {
+                        "ywebsocket_server": self.ywebsocket_server,
+                    }
+                ),
             ]
         )
 
diff --git a/jupyter_collaboration/handlers.py b/jupyter_collaboration/handlers.py
index 81b64b3d..af12972a 100644
--- a/jupyter_collaboration/handlers.py
+++ b/jupyter_collaboration/handlers.py
@@ -6,13 +6,14 @@
 import asyncio
 import json
 import time
-import uuid
+from uuid import uuid4
 from typing import Any
 
 from jupyter_server.auth import authorized
 from jupyter_server.base.handlers import APIHandler, JupyterHandler
 from jupyter_ydoc import ydocs as YDOCS
-from pycrdt_websocket.websocket_server import YRoom
+from pycrdt import Doc, Map
+from pycrdt_websocket.yroom import YRoom
 from pycrdt_websocket.ystore import BaseYStore
 from pycrdt_websocket.yutils import YMessageType, write_var_uint
 from tornado import web
@@ -31,7 +32,7 @@
 
 YFILE = YDOCS["file"]
 
-SERVER_SESSION = str(uuid.uuid4())
+SERVER_SESSION = str(uuid4())
 
 
 class YDocWebSocketHandler(WebSocketHandler, JupyterHandler):
@@ -404,3 +405,119 @@ async def put(self, path):
         )
         self.set_status(201)
         return self.finish(data)
+
+
+class DocForkHandler(APIHandler):
+    """
+    Jupyter Server's handler to fork a document.
+    """
+
+    auth_resource = "contents"
+
+    def initialize(
+        self,
+        ywebsocket_server: JupyterWebsocketServer,
+    ) -> None:
+        self._websocket_server = ywebsocket_server
+
+    @web.authenticated
+    @authorized
+    async def put(self, room_id):
+        """
+        Creates a fork of a root document and returns its ID.
+        """
+        idx = uuid4().hex
+
+        root_room = await self._websocket_server.get_room(room_id)
+        update = root_room.ydoc.get_update()
+        fork_ydoc = Doc()
+        fork_ydoc.apply_update(update)
+        fork_room = YRoom(ydoc=fork_ydoc)
+        self._websocket_server.add_room(idx, fork_room)
+        root_room.fork_ydocs.add(fork_ydoc)
+        data = json.dumps({
+            "sessionId": SERVER_SESSION,
+            "roomId": idx,
+        })
+        self.set_status(201)
+        return self.finish(data)
+
+
+class DocMergeHandler(APIHandler):
+    """
+    Jupyter Server's handler to merge a document.
+    """
+
+    auth_resource = "contents"
+
+    def initialize(
+        self,
+        ywebsocket_server: JupyterWebsocketServer,
+    ) -> None:
+        self._websocket_server = ywebsocket_server
+
+    @web.authenticated
+    @authorized
+    async def put(self):
+        """
+        Merges back a fork into a root document.
+        """
+        model = self.get_json_body()
+        fork_roomid = model["fork_roomid"]
+        root_room = await self._websocket_server.get_room(model["root_roomid"])
+        root_ydoc = root_room.ydoc
+        idx = f"fork_{fork_roomid}"
+        root_state = root_ydoc.get("state", type=Map)
+        if idx in root_state:
+            del root_state[idx]
+        else:
+            self.set_status(404)
+            raise RuntimeError(f"Could not find root document fork with ID: {fork_roomid}")
+        fork_room = await self._websocket_server.get_room(fork_roomid)
+        fork_ydoc = fork_room.ydoc
+        fork_update = fork_ydoc.get_update()
+        root_ydoc.apply_update(fork_update)
+        root_room.fork_ydocs.remove(fork_ydoc)
+        fork_state = fork_ydoc.get("state", type=Map)
+        fork_state["merge"] = fork_roomid
+        #self._websocket_server.delete_room(name=fork_roomid)
+        self.set_status(200)
+
+
+class DocDeleteHandler(APIHandler):
+    """
+    Jupyter Server's handler to delete a document.
+    """
+
+    auth_resource = "contents"
+
+    def initialize(
+        self,
+        ywebsocket_server: JupyterWebsocketServer,
+    ) -> None:
+        self._websocket_server = ywebsocket_server
+
+    @web.authenticated
+    @authorized
+    async def delete(self):
+        """
+        Deletes a forked document.
+        """
+        model = self.get_json_body()
+        fork_roomid = model["fork_roomid"]
+        root_room = await self._websocket_server.get_room(model["root_roomid"])
+        root_ydoc = root_room.ydoc
+        idx = f"fork_{fork_roomid}"
+        root_state = root_ydoc.get("state", type=Map)
+        if idx in root_state:
+            del root_state[idx]
+        else:
+            self.set_status(404)
+            raise RuntimeError(f"Could not find root document fork with ID: {fork_roomid}")
+        fork_room = await self._websocket_server.get_room(fork_roomid)
+        fork_ydoc = fork_room.ydoc
+        root_room.fork_ydocs.remove(fork_ydoc)
+        fork_state = fork_ydoc.get("state", type=Map)
+        fork_state["delete"] = fork_roomid
+        #self._websocket_server.delete_room(name=fork_roomid)
+        self.set_status(200)
diff --git a/package.json b/package.json
index 1bad1fa0..6b8906de 100644
--- a/package.json
+++ b/package.json
@@ -65,5 +65,8 @@
     "stylelint-prettier": "^3.0.0",
     "typedoc": "~0.23.28",
     "typescript": "~5.0.4"
+  },
+  "resolutions": {
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc"
   }
 }
diff --git a/packages/collaboration-extension/package.json b/packages/collaboration-extension/package.json
index e8812ce1..76f3b77a 100644
--- a/packages/collaboration-extension/package.json
+++ b/packages/collaboration-extension/package.json
@@ -55,7 +55,7 @@
   "dependencies": {
     "@jupyter/collaboration": "^2.0.11",
     "@jupyter/docprovider": "^2.0.11",
-    "@jupyter/ydoc": "^1.1.0-a0",
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc",
     "@jupyterlab/application": "^4.0.5",
     "@jupyterlab/apputils": "^4.0.5",
     "@jupyterlab/codemirror": "^4.0.5",
diff --git a/packages/collaboration-extension/src/collaboration.ts b/packages/collaboration-extension/src/collaboration.ts
index e2502bca..783684f1 100644
--- a/packages/collaboration-extension/src/collaboration.ts
+++ b/packages/collaboration-extension/src/collaboration.ts
@@ -5,25 +5,43 @@
  * @module collaboration-extension
  */
 
+import {
+  DocumentRegistry
+} from '@jupyterlab/docregistry';
+
+import {
+  NotebookPanel, INotebookModel
+} from '@jupyterlab/notebook';
+
+import {
+  IDisposable, DisposableDelegate
+} from '@lumino/disposable';
+
+import { CommandRegistry } from '@lumino/commands';
+
 import {
   JupyterFrontEnd,
   JupyterFrontEndPlugin
 } from '@jupyterlab/application';
-import { IToolbarWidgetRegistry } from '@jupyterlab/apputils';
+import { Dialog, IToolbarWidgetRegistry } from '@jupyterlab/apputils';
 import {
   EditorExtensionRegistry,
   IEditorExtensionRegistry
 } from '@jupyterlab/codemirror';
-import { WebSocketAwarenessProvider } from '@jupyter/docprovider';
-import { SidePanel, usersIcon } from '@jupyterlab/ui-components';
+import { requestDocDelete, requestDocMerge, WebSocketAwarenessProvider } from '@jupyter/docprovider';
+import {
+  SidePanel,
+  usersIcon,
+  caretDownIcon
+} from '@jupyterlab/ui-components';
 import { URLExt } from '@jupyterlab/coreutils';
 import { ServerConnection } from '@jupyterlab/services';
 import { IStateDB, StateDB } from '@jupyterlab/statedb';
-import { ITranslator, nullTranslator } from '@jupyterlab/translation';
+import { ITranslator, nullTranslator, TranslationBundle } from '@jupyterlab/translation';
 
 import { Menu, MenuBar } from '@lumino/widgets';
 
-import { IAwareness } from '@jupyter/ydoc';
+import { IAwareness, ISharedNotebook, NotebookChange } from '@jupyter/ydoc';
 
 import {
   CollaboratorsPanel,
@@ -189,3 +207,221 @@ export const userEditorCursors: JupyterFrontEndPlugin<void> = {
     });
   }
 };
+
+/**
+ * A plugin to add editing mode to the notebook page
+ */
+export const editingMode: JupyterFrontEndPlugin<void> = {
+  id: '@jupyter/collaboration-extension:editingMode',
+  description: 'A plugin to add editing mode to the notebook page.',
+  autoStart: true,
+  optional: [ITranslator],
+  activate: (
+    app: JupyterFrontEnd,
+    translator: ITranslator | null
+  ) => {
+    app.docRegistry.addWidgetExtension('Notebook', new EditingModeExtension(translator));
+  },
+};
+
+export class EditingModeExtension implements DocumentRegistry.IWidgetExtension<NotebookPanel, INotebookModel> {
+  private _trans: TranslationBundle;
+
+  constructor(translator: ITranslator | null) {
+    this._trans = (translator ?? nullTranslator).load('jupyter_collaboration');
+  }
+
+  createNew(
+    panel: NotebookPanel,
+    context: DocumentRegistry.IContext<INotebookModel>
+  ): IDisposable {
+    const editingMenubar = new MenuBar();
+    const suggestionMenubar = new MenuBar();
+    const reviewMenubar = new MenuBar();
+
+    const editingCommands = new CommandRegistry();
+    const suggestionCommands = new CommandRegistry();
+    const reviewCommands = new CommandRegistry();
+
+    const editingMenu = new Menu({ commands: editingCommands });
+    const suggestionMenu = new Menu({ commands: suggestionCommands });
+    const reviewMenu = new Menu({ commands: reviewCommands });
+
+    const sharedModel = context.model.sharedModel;
+    const suggestions: {[key: string]: Menu.IItem} = {};
+    var myForkId = '';  // curently allows only one suggestion per user
+
+    editingMenu.title.label = 'Editing';
+    editingMenu.title.icon = caretDownIcon;
+
+    suggestionMenu.title.label = 'Root';
+    suggestionMenu.title.icon = caretDownIcon;
+
+    reviewMenu.title.label = 'Review';
+    reviewMenu.title.icon = caretDownIcon;
+
+    editingCommands.addCommand('editing', {
+      label: 'Editing',
+      execute: () => {
+        editingMenu.title.label = 'Editing';
+        suggestionMenu.title.label = 'Root';
+        open_dialog('Editing', this._trans);
+      }
+    });
+    editingCommands.addCommand('suggesting', {
+      label: 'Suggesting',
+      execute: () => {
+        editingMenu.title.label = 'Suggesting';
+        reviewMenu.clearItems();
+        if (myForkId === '') {
+          myForkId = 'pending';
+          sharedModel.provider.fork().then(newForkId => {
+            myForkId = newForkId;
+            sharedModel.provider.connect(newForkId);
+            suggestionMenu.title.label = newForkId;
+          });
+        }
+        else {
+          suggestionMenu.title.label = myForkId;
+          sharedModel.provider.connect(myForkId);
+        }
+        open_dialog('Suggesting', this._trans);
+      }
+    });
+
+    suggestionCommands.addCommand('root', {
+      label: 'Root',
+      execute: () => {
+        // we cannot review the root document
+        reviewMenu.clearItems();
+        suggestionMenu.title.label = 'Root';
+        editingMenu.title.label = 'Editing';
+        sharedModel.provider.connect(sharedModel.rootRoomId);
+        open_dialog('Editing', this._trans);
+      }
+    });
+
+    reviewCommands.addCommand('merge', {
+      label: 'Merge',
+      execute: () => {
+        requestDocMerge(sharedModel.currentRoomId, sharedModel.rootRoomId);
+      }
+    });
+    reviewCommands.addCommand('discard', {
+      label: 'Discard',
+      execute: () => {
+        requestDocDelete(sharedModel.currentRoomId, sharedModel.rootRoomId);
+      }
+    });
+
+    editingMenu.addItem({type: 'command', command: 'editing'});
+    editingMenu.addItem({type: 'command', command: 'suggesting'});
+
+    suggestionMenu.addItem({type: 'command', command: 'root'});
+
+    const _onStateChanged = (sender: ISharedNotebook, changes: NotebookChange) => {
+      if (changes.stateChange) {
+        changes.stateChange.forEach(value => {
+          const forkPrefix = 'fork_';
+          if (value.name === 'merge' || value.name === 'delete') {
+            // we are on fork
+            if (sharedModel.currentRoomId === value.newValue) {
+              reviewMenu.clearItems();
+              const merge = value.name === 'merge';
+              sharedModel.provider.connect(sharedModel.rootRoomId, merge);
+              open_dialog('Editing', this._trans);
+              myForkId = '';
+            }
+          }
+          else if (value.name.startsWith(forkPrefix)) {
+            // we are on root
+            const forkId = value.name.slice(forkPrefix.length);
+            if (value.newValue === 'new') {
+              suggestionCommands.addCommand(forkId, {
+                label: forkId,
+                execute: () => {
+                  editingMenu.title.label = 'Suggesting';
+                  reviewMenu.clearItems();
+                  reviewMenu.addItem({type: 'command', command: 'merge'});
+                  reviewMenu.addItem({type: 'command', command: 'discard'});
+                  suggestionMenu.title.label = forkId;
+                  sharedModel.provider.connect(forkId);
+                  open_dialog('Suggesting', this._trans);
+                }
+              });
+              const item = suggestionMenu.addItem({type: 'command', command: forkId});
+              suggestions[forkId] = item;
+              if (myForkId !== forkId) {
+                if (myForkId !== 'pending') {
+                  const dialog = new Dialog({
+                    title: this._trans.__('New suggestion'),
+                    body: this._trans.__('View suggestion?'),
+                    buttons: [
+                      Dialog.okButton({ label: 'View' }),
+                      Dialog.cancelButton({ label: 'Discard' }),
+                    ],
+                  });
+                  dialog.launch().then(resp => {
+                    dialog.close();
+                    if (resp.button.label === 'View') {
+                      sharedModel.provider.connect(forkId);
+                      suggestionMenu.title.label = forkId;
+                      editingMenu.title.label = 'Suggesting';
+                      reviewMenu.clearItems();
+                      reviewMenu.addItem({type: 'command', command: 'merge'});
+                      reviewMenu.addItem({type: 'command', command: 'discard'});
+                    }
+                  });
+                }
+                else {
+                  reviewMenu.clearItems();
+                  reviewMenu.addItem({type: 'command', command: 'merge'});
+                  reviewMenu.addItem({type: 'command', command: 'discard'});
+                }
+              }
+            }
+            else if (value.newValue === undefined) {
+              editingMenu.title.label = 'Editing';
+              suggestionMenu.title.label = 'Root';
+              const item: Menu.IItem = suggestions[value.oldValue];
+              delete suggestions[value.oldValue];
+              suggestionMenu.removeItem(item);
+            }
+          }
+        });
+      }
+    };
+
+    sharedModel.changed.connect(_onStateChanged, this);
+
+    editingMenubar.addMenu(editingMenu);
+    suggestionMenubar.addMenu(suggestionMenu);
+    reviewMenubar.addMenu(reviewMenu);
+
+    panel.toolbar.insertItem(997, 'editingMode', editingMenubar);
+    panel.toolbar.insertItem(998, 'suggestions', suggestionMenubar);
+    panel.toolbar.insertItem(999, 'review', reviewMenubar);
+    return new DisposableDelegate(() => {
+      editingMenubar.dispose();
+      suggestionMenubar.dispose();
+      reviewMenubar.dispose();
+    });
+  }
+}
+
+
+function open_dialog(title: string, trans: TranslationBundle) {
+  var body: string;
+  if (title === 'Editing') {
+    body = 'You are now directly editing the document.'
+  }
+  else {
+    body = 'Your edits now become suggestions to the document.'
+  }
+  const dialog = new Dialog({
+    title: trans.__(title),
+    body: trans.__(body),
+    buttons: [Dialog.okButton({ label: 'OK' })],
+  });
+  dialog.launch().then(resp => { dialog.close(); });
+}
diff --git a/packages/collaboration-extension/src/index.ts b/packages/collaboration-extension/src/index.ts
index 513befa1..3e1be19b 100644
--- a/packages/collaboration-extension/src/index.ts
+++ b/packages/collaboration-extension/src/index.ts
@@ -19,7 +19,8 @@ import {
   menuBarPlugin,
   rtcGlobalAwarenessPlugin,
   rtcPanelPlugin,
-  userEditorCursors
+  userEditorCursors,
+  editingMode
 } from './collaboration';
 import { sharedLink } from './sharedlink';
 
@@ -37,7 +38,8 @@ const plugins: JupyterFrontEndPlugin<any>[] = [
   rtcGlobalAwarenessPlugin,
   rtcPanelPlugin,
   sharedLink,
-  userEditorCursors
+  userEditorCursors,
+  editingMode
 ];
 
 export default plugins;
diff --git a/packages/collaboration/package.json b/packages/collaboration/package.json
index 1f813402..8cebcff2 100644
--- a/packages/collaboration/package.json
+++ b/packages/collaboration/package.json
@@ -42,6 +42,7 @@
     "@codemirror/state": "^6.2.0",
     "@codemirror/view": "^6.7.0",
     "@jupyter/docprovider": "^2.0.11",
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc",
     "@jupyterlab/apputils": "^4.0.5",
     "@jupyterlab/coreutils": "^6.0.5",
     "@jupyterlab/services": "^7.0.5",
diff --git a/packages/docprovider/package.json b/packages/docprovider/package.json
index fec4a135..47fa53d0 100644
--- a/packages/docprovider/package.json
+++ b/packages/docprovider/package.json
@@ -41,7 +41,7 @@
     "watch": "tsc -b --watch"
   },
   "dependencies": {
-    "@jupyter/ydoc": "^1.1.0-a0",
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc",
     "@jupyterlab/coreutils": "^6.0.5",
     "@jupyterlab/services": "^7.0.5",
     "@lumino/coreutils": "^2.1.0",
@@ -51,6 +51,10 @@
     "y-websocket": "^1.3.15",
     "yjs": "^13.5.40"
   },
+  "resolutions": {
+    "@jupyterlab/services": "file:.yalc/@jupyterlab/services",
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc"
+  },
   "devDependencies": {
     "@jupyterlab/testing": "^4.0.5",
     "@types/jest": "^29.2.0",
diff --git a/packages/docprovider/src/index.ts b/packages/docprovider/src/index.ts
index 62edebda..abfd4873 100644
--- a/packages/docprovider/src/index.ts
+++ b/packages/docprovider/src/index.ts
@@ -8,6 +8,7 @@
  */
 
 export * from './awareness';
+export * from './requests';
 export * from './ydrive';
 export * from './yprovider';
 export * from './tokens';
diff --git a/packages/docprovider/src/requests.ts b/packages/docprovider/src/requests.ts
index 54e7c364..699f2a65 100644
--- a/packages/docprovider/src/requests.ts
+++ b/packages/docprovider/src/requests.ts
@@ -11,6 +11,9 @@ import { ServerConnection, Contents } from '@jupyterlab/services';
  * See https://github.com/jupyterlab/jupyter_collaboration
  */
 const DOC_SESSION_URL = 'api/collaboration/session';
+const DOC_FORK_URL = 'api/collaboration/fork_room';
+const DOC_MERGE_URL = 'api/collaboration/merge_room';
+const DOC_DELETE_URL = 'api/collaboration/delete_room';
 
 /**
  * Document session model
@@ -73,3 +76,117 @@ export async function requestDocSession(
 
   return data;
 }
+
+
+export async function requestDocFork(
+  roomid: string,
+): Promise<any> {
+  const settings = ServerConnection.makeSettings();
+  const url = URLExt.join(
+    settings.baseUrl,
+    DOC_FORK_URL,
+    encodeURIComponent(roomid)
+  );
+  const body = {method: 'PUT'};
+
+  let response: Response;
+  try {
+    response = await ServerConnection.makeRequest(url, body, settings);
+  } catch (error) {
+    throw new ServerConnection.NetworkError(error as Error);
+  }
+
+  let data: any = await response.text();
+
+  if (data.length > 0) {
+    try {
+      data = JSON.parse(data);
+    } catch (error) {
+      console.log('Not a JSON response body.', response);
+    }
+  }
+
+  if (!response.ok) {
+    throw new ServerConnection.ResponseError(response, data.message || data);
+  }
+
+  return data;
+}
+
+
+export async function requestDocMerge(
+  forkRoomid: string,
+  rootRoomid: string
+): Promise<any> {
+  const settings = ServerConnection.makeSettings();
+  const url = URLExt.join(
+    settings.baseUrl,
+    DOC_MERGE_URL
+  );
+  const body = {
+    method: 'PUT',
+    body: JSON.stringify({ fork_roomid: forkRoomid, root_roomid: rootRoomid })
+  };
+
+  let response: Response;
+  try {
+    response = await ServerConnection.makeRequest(url, body, settings);
+  } catch (error) {
+    throw new ServerConnection.NetworkError(error as Error);
+  }
+
+  let data: any = await response.text();
+
+  if (data.length > 0) {
+    try {
+      data = JSON.parse(data);
+    } catch (error) {
+      console.log('Not a JSON response body.', response);
+    }
+  }
+
+  if (!response.ok) {
+    throw new ServerConnection.ResponseError(response, data.message || data);
+  }
+
+  return data;
+}
+
+
+export async function requestDocDelete(
+  forkRoomid: string,
+  rootRoomid: string,
+): Promise<any> {
+  const settings = ServerConnection.makeSettings();
+  const url = URLExt.join(
+    settings.baseUrl,
+    DOC_DELETE_URL,
+  );
+  const body = {
+    method: 'DELETE',
+    body: JSON.stringify({ fork_roomid: forkRoomid, root_roomid: rootRoomid })
+  };
+
+  let response: Response;
+  try {
+    response = await ServerConnection.makeRequest(url, body, settings);
+  } catch (error) {
+    throw new ServerConnection.NetworkError(error as Error);
+  }
+
+  let data: any = await response.text();
+
+  if (data.length > 0) {
+    try {
+      data = JSON.parse(data);
+    } catch (error) {
+      console.log('Not a JSON response body.', response);
+    }
+  }
+
+  if (!response.ok) {
+    throw new ServerConnection.ResponseError(response, data.message || data);
+  }
+
+  return data;
+}
diff --git a/packages/docprovider/src/ydrive.ts b/packages/docprovider/src/ydrive.ts
index b8ec4d60..aab5b43c 100644
--- a/packages/docprovider/src/ydrive.ts
+++ b/packages/docprovider/src/ydrive.ts
@@ -147,6 +147,7 @@ export class YDrive extends Drive implements ICollaborativeDrive {
       const key = `${options.format}:${options.contentType}:${options.path}`;
       this._providers.set(key, provider);
 
+      sharedModel.provider = provider;
       sharedModel.disposed.connect(() => {
         const provider = this._providers.get(key);
         if (provider) {
diff --git a/packages/docprovider/src/yprovider.ts b/packages/docprovider/src/yprovider.ts
index 4061ebeb..a3990adc 100644
--- a/packages/docprovider/src/yprovider.ts
+++ b/packages/docprovider/src/yprovider.ts
@@ -8,25 +8,15 @@ import { User } from '@jupyterlab/services';
 import { TranslationBundle } from '@jupyterlab/translation';
 
 import { PromiseDelegate } from '@lumino/coreutils';
-import { IDisposable } from '@lumino/disposable';
 import { Signal } from '@lumino/signaling';
 
-import { DocumentChange, YDocument } from '@jupyter/ydoc';
+import { DocumentChange, IDocumentProvider, YDocument } from '@jupyter/ydoc';
 
 import { Awareness } from 'y-protocols/awareness';
 import { WebsocketProvider as YWebsocketProvider } from 'y-websocket';
 
-import { requestDocSession } from './requests';
+import { requestDocFork, requestDocSession } from './requests';
 
-/**
- * An interface for a document provider.
- */
-export interface IDocumentProvider extends IDisposable {
-  /**
-   * Returns a Promise that resolves when the document provider is ready.
-   */
-  readonly ready: Promise<void>;
-}
 
 /**
  * A class to provide Yjs synchronization over WebSocket.
@@ -42,6 +32,7 @@ export class WebSocketProvider implements IDocumentProvider {
    */
   constructor(options: WebSocketProvider.IOptions) {
     this._isDisposed = false;
+    this._sessionId = options.sessionId ?? '';
     this._path = options.path;
     this._contentType = options.contentType;
     this._format = options.format;
@@ -50,15 +41,14 @@ export class WebSocketProvider implements IDocumentProvider {
     this._awareness = options.model.awareness;
     this._yWebsocketProvider = null;
     this._trans = options.translator;
+    this._user = options.user;
 
-    const user = options.user;
-
-    user.ready
+    this._user.ready
       .then(() => {
-        this._onUserChanged(user);
+        this._onUserChanged(this._user);
       })
       .catch(e => console.error(e));
-    user.userChanged.connect(this._onUserChanged, this);
+    this._user.userChanged.connect(this._onUserChanged, this);
 
     this._connect().catch(e => console.warn(e));
   }
@@ -91,20 +81,71 @@ export class WebSocketProvider implements IDocumentProvider {
     Signal.clearData(this);
   }
 
-  private async _connect(): Promise<void> {
+  async fork(): Promise<string> {
     const session = await requestDocSession(
       this._format,
       this._contentType,
       this._path
     );
 
+    const response = await requestDocFork(`${session.format}:${session.type}:${session.fileId}`);
+    const forkId = response.roomId;
+    this._sharedModel.currentRoomId = forkId;
+    this._sharedModel.addFork(forkId);
+
+    return forkId;
+  }
+
+  connect(roomId: string, merge?: boolean) {
+    this._sharedModel.currentRoomId = roomId;
+    this._yWebsocketProvider?.disconnect();
+    if (roomId === this._sharedModel.rootRoomId) {
+      // connecting to the root
+      // don't bring our changes there if not merging
+      if (merge !== true) {
+        while (this._sharedModel.undoManager.canUndo()) {
+          this._sharedModel.undoManager.undo();
+        }
+      }
+      this._sharedModel.undoManager.clear();
+    }
+    else {
+      // connecting to a fork
+      // keep track of changes so that we can undo them when connecting back to root
+      this._sharedModel.undoManager.clear();
+    }
+
+    this._yWebsocketProvider = new YWebsocketProvider(
+      this._serverUrl,
+      roomId,
+      this._sharedModel.ydoc,
+      {
+        disableBc: true,
+        params: { sessionId: this._sessionId },
+        awareness: this._awareness
+      }
+    );
+  }
+
+  private async _connect(): Promise<void> {
+    if (this._sharedModel.rootRoomId === '') {
+      const session = await requestDocSession(
+        this._format,
+        this._contentType,
+        this._path
+      );
+      this._sharedModel.rootRoomId = `${session.format}:${session.type}:${session.fileId}`;
+      this._sharedModel.currentRoomId = this._sharedModel.rootRoomId;
+      this._sessionId = session.sessionId;
+    }
+
     this._yWebsocketProvider = new YWebsocketProvider(
       this._serverUrl,
-      `${session.format}:${session.type}:${session.fileId}`,
+      this._sharedModel.rootRoomId,
       this._sharedModel.ydoc,
       {
         disableBc: true,
-        params: { sessionId: session.sessionId },
+        params: { sessionId: this._sessionId! },
         awareness: this._awareness
       }
     );
@@ -142,12 +183,14 @@ export class WebSocketProvider implements IDocumentProvider {
   private _contentType: string;
   private _format: string;
   private _isDisposed: boolean;
+  private _sessionId: string;
   private _path: string;
   private _ready = new PromiseDelegate<void>();
   private _serverUrl: string;
   private _sharedModel: YDocument<DocumentChange>;
   private _yWebsocketProvider: YWebsocketProvider | null;
   private _trans: TranslationBundle;
+  private _user: User.IManager;
 }
 
 /**
@@ -192,5 +235,10 @@ export namespace WebSocketProvider {
      * The jupyterlab translator
      */
     translator: TranslationBundle;
+
+    /**
+     * The document session ID, if the document is a fork
+     */
+    sessionId?: string;
   }
 }
diff --git a/yarn.lock b/yarn.lock
index f52db1a8..2797ea8d 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -2035,7 +2035,7 @@ __metadata:
   dependencies:
     "@jupyter/collaboration": ^2.0.11
     "@jupyter/docprovider": ^2.0.11
-    "@jupyter/ydoc": ^1.1.0-a0
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc"
     "@jupyterlab/application": ^4.0.5
     "@jupyterlab/apputils": ^4.0.5
     "@jupyterlab/builder": ^4.0.5
@@ -2070,6 +2070,7 @@ __metadata:
     "@codemirror/state": ^6.2.0
     "@codemirror/view": ^6.7.0
     "@jupyter/docprovider": ^2.0.11
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc"
     "@jupyterlab/apputils": ^4.0.5
     "@jupyterlab/coreutils": ^6.0.5
     "@jupyterlab/services": ^7.0.5
@@ -2090,7 +2091,7 @@ __metadata:
   version: 0.0.0-use.local
   resolution: "@jupyter/docprovider@workspace:packages/docprovider"
   dependencies:
-    "@jupyter/ydoc": ^1.1.0-a0
+    "@jupyter/ydoc": "file:.yalc/@jupyter/ydoc"
     "@jupyterlab/coreutils": ^6.0.5
     "@jupyterlab/services": ^7.0.5
     "@jupyterlab/testing": ^4.0.5
@@ -2107,6 +2108,17 @@ __metadata:
   languageName: unknown
   linkType: soft
 
+"@jupyter/react-components@npm:^0.15.2":
+  version: 0.15.2
+  resolution: "@jupyter/react-components@npm:0.15.2"
+  dependencies:
+    "@jupyter/web-components": ^0.15.2
+    "@microsoft/fast-react-wrapper": ^0.3.22
+    react: ">=17.0.0 <19.0.0"
+  checksum: d6d339ff9c2fed1fd5afda612be500d73c4a83eee5470d50e94020dadd1e389a3bf745c7240b0a48edbc6d3fdacec93367b7b5e40588f2df588419caada705be
+  languageName: node
+  linkType: hard
+
 "@jupyter/real-time-collaboration@workspace:.":
   version: 0.0.0-use.local
   resolution: "@jupyter/real-time-collaboration@workspace:."
@@ -2130,31 +2142,58 @@ __metadata:
   languageName: unknown
   linkType: soft
 
-"@jupyter/ydoc@npm:^1.0.2":
-  version: 1.0.2
-  resolution: "@jupyter/ydoc@npm:1.0.2"
+"@jupyter/web-components@npm:^0.15.2":
+  version: 0.15.2
+  resolution: "@jupyter/web-components@npm:0.15.2"
   dependencies:
-    "@jupyterlab/nbformat": ^3.0.0 || ^4.0.0-alpha.21 || ^4.0.0
-    "@lumino/coreutils": ^1.11.0 || ^2.0.0
-    "@lumino/disposable": ^1.10.0 || ^2.0.0
-    "@lumino/signaling": ^1.10.0 || ^2.0.0
-    y-protocols: ^1.0.5
-    yjs: ^13.5.40
-  checksum: 739f9630940466b3cfcd7b742dd06479f81772ca13f863d057af0bbb5e318829506969066ab72977e7c721644982b5c8f88cf44e1ae81955ed1c27e87632d1f2
+    "@microsoft/fast-colors": ^5.3.1
+    "@microsoft/fast-element": ^1.12.0
+    "@microsoft/fast-foundation": ^2.49.4
+    "@microsoft/fast-web-utilities": ^5.4.1
+  checksum: f272ef91de08e28f9414a26dbd2388e1a8985c90f4ab00231978cee49bd5212f812411397a9038d298c8c0c4b41eb28cc86f1127bc7ace309bda8df60c4a87c8
   languageName: node
   linkType: hard
 
-"@jupyter/ydoc@npm:^1.1.0-a0":
-  version: 1.1.0-a0
-  resolution: "@jupyter/ydoc@npm:1.1.0-a0"
+"@jupyter/ydoc@file:.yalc/@jupyter/ydoc::locator=%40jupyter%2Freal-time-collaboration%40workspace%3A.":
+  version: 2.0.1
+  resolution: "@jupyter/ydoc@file:.yalc/@jupyter/ydoc#.yalc/@jupyter/ydoc::hash=045bce&locator=%40jupyter%2Freal-time-collaboration%40workspace%3A."
   dependencies:
+    "@jupyterlab/application": ^4.0.0
     "@jupyterlab/nbformat": ^3.0.0 || ^4.0.0-alpha.21 || ^4.0.0
     "@lumino/coreutils": ^1.11.0 || ^2.0.0
     "@lumino/disposable": ^1.10.0 || ^2.0.0
     "@lumino/signaling": ^1.10.0 || ^2.0.0
     y-protocols: ^1.0.5
     yjs: ^13.5.40
-  checksum: 0099bacb2884a460867658e7f5a944e4d6eca7c4d3d68a6b31102be77d8fc9b6ba162af55c20f81c70f7fef4e9d9329eee4da32063c0caa0c6e3f10a488f95b5
+  checksum: aed2b93d1f9d447e7ad1be8699dc3a31968f4cfd4772a1ed1330308eb08ba8d14973df24bae4e49bd93f416f646b84edb44c567487403e7d0bdb665e6ca0e29f
+  languageName: node
+  linkType: hard
+
+"@jupyterlab/application@npm:^4.0.0":
+  version: 4.1.2
+  resolution: "@jupyterlab/application@npm:4.1.2"
+  dependencies:
+    "@fortawesome/fontawesome-free": ^5.12.0
+    "@jupyterlab/apputils": ^4.2.2
+    "@jupyterlab/coreutils": ^6.1.2
+    "@jupyterlab/docregistry": ^4.1.2
+    "@jupyterlab/rendermime": ^4.1.2
+    "@jupyterlab/rendermime-interfaces": ^3.9.2
+    "@jupyterlab/services": ^7.1.2
+    "@jupyterlab/statedb": ^4.1.2
+    "@jupyterlab/translation": ^4.1.2
+    "@jupyterlab/ui-components": ^4.1.2
+    "@lumino/algorithm": ^2.0.1
+    "@lumino/application": ^2.3.0
+    "@lumino/commands": ^2.2.0
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/messaging": ^2.0.1
+    "@lumino/polling": ^2.1.2
+    "@lumino/properties": ^2.0.1
+    "@lumino/signaling": ^2.1.2
+    "@lumino/widgets": ^2.3.1
+  checksum: 10be4cdfd08dfd69786a3cd9753d48246e507e6a1cf15572bc4938be1d53c5c3fe291153ff02f2ffc941f77ab3c648649a6e6e2db6bbbcfcaa1bcc17a525b90b
   languageName: node
   linkType: hard
 
@@ -2215,6 +2254,35 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/apputils@npm:^4.2.2":
+  version: 4.2.2
+  resolution: "@jupyterlab/apputils@npm:4.2.2"
+  dependencies:
+    "@jupyterlab/coreutils": ^6.1.2
+    "@jupyterlab/observables": ^5.1.2
+    "@jupyterlab/rendermime-interfaces": ^3.9.2
+    "@jupyterlab/services": ^7.1.2
+    "@jupyterlab/settingregistry": ^4.1.2
+    "@jupyterlab/statedb": ^4.1.2
+    "@jupyterlab/statusbar": ^4.1.2
+    "@jupyterlab/translation": ^4.1.2
+    "@jupyterlab/ui-components": ^4.1.2
+    "@lumino/algorithm": ^2.0.1
+    "@lumino/commands": ^2.2.0
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/domutils": ^2.0.1
+    "@lumino/messaging": ^2.0.1
+    "@lumino/signaling": ^2.1.2
+    "@lumino/virtualdom": ^2.0.1
+    "@lumino/widgets": ^2.3.1
+    "@types/react": ^18.0.26
+    react: ^18.2.0
+    sanitize-html: ~2.7.3
+  checksum: 6d0811f30ba353d9ce67d515fdfff802f99a628b7403b4b7aa44291d634bd228c0073ddab5ed6d160eb7bdc214b23e540039c1c5fd1f76ba9635b4ca3cca1d30
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/attachments@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/attachments@npm:4.0.5"
@@ -2329,6 +2397,30 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/codeeditor@npm:^4.1.2":
+  version: 4.1.2
+  resolution: "@jupyterlab/codeeditor@npm:4.1.2"
+  dependencies:
+    "@codemirror/state": ^6.2.0
+    "@jupyter/ydoc": ^1.1.1
+    "@jupyterlab/apputils": ^4.2.2
+    "@jupyterlab/coreutils": ^6.1.2
+    "@jupyterlab/nbformat": ^4.1.2
+    "@jupyterlab/observables": ^5.1.2
+    "@jupyterlab/statusbar": ^4.1.2
+    "@jupyterlab/translation": ^4.1.2
+    "@jupyterlab/ui-components": ^4.1.2
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/dragdrop": ^2.1.4
+    "@lumino/messaging": ^2.0.1
+    "@lumino/signaling": ^2.1.2
+    "@lumino/widgets": ^2.3.1
+    react: ^18.2.0
+  checksum: b09618bc80a6d62c11fe53ccfe51cae1bdeb7298fab00c71a1119efa8102b86b6aa828d75b00ede80821b7073e3d6c3bb48c93805572eef4563308e4d3e7da1e
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/codemirror@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/codemirror@npm:4.0.5"
@@ -2385,6 +2477,34 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/coreutils@npm:^6.1.2":
+  version: 6.1.2
+  resolution: "@jupyterlab/coreutils@npm:6.1.2"
+  dependencies:
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/signaling": ^2.1.2
+    minimist: ~1.2.0
+    path-browserify: ^1.0.0
+    url-parse: ~1.5.4
+  checksum: 6dcc812e0ebae28f902ece4acd58aee8103033b23a3bac0935d4d9d8c9c10f8797b422f4e8b0be53fac4781811fb9b82874ce499cd69a6d198986e0cdb4a97ff
+  languageName: node
+  linkType: hard
+
+"@jupyterlab/coreutils@npm:^6.1.5":
+  version: 6.1.5
+  resolution: "@jupyterlab/coreutils@npm:6.1.5"
+  dependencies:
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/signaling": ^2.1.2
+    minimist: ~1.2.0
+    path-browserify: ^1.0.0
+    url-parse: ~1.5.4
+  checksum: b91c5a374f3c97d62e2442bb5f12cb79c6e440b5f6aa4d4ed6e492e8ca38836f7068106bb7029834a4e5de1947a9c44c342d23bedf9a4611aafca33629aed049
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/docmanager@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/docmanager@npm:4.0.5"
@@ -2433,6 +2553,32 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/docregistry@npm:^4.1.2":
+  version: 4.1.2
+  resolution: "@jupyterlab/docregistry@npm:4.1.2"
+  dependencies:
+    "@jupyter/ydoc": ^1.1.1
+    "@jupyterlab/apputils": ^4.2.2
+    "@jupyterlab/codeeditor": ^4.1.2
+    "@jupyterlab/coreutils": ^6.1.2
+    "@jupyterlab/observables": ^5.1.2
+    "@jupyterlab/rendermime": ^4.1.2
+    "@jupyterlab/rendermime-interfaces": ^3.9.2
+    "@jupyterlab/services": ^7.1.2
+    "@jupyterlab/translation": ^4.1.2
+    "@jupyterlab/ui-components": ^4.1.2
+    "@lumino/algorithm": ^2.0.1
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/messaging": ^2.0.1
+    "@lumino/properties": ^2.0.1
+    "@lumino/signaling": ^2.1.2
+    "@lumino/widgets": ^2.3.1
+    react: ^18.2.0
+  checksum: 6dcef927286f66636d8f7f0a128d7c5084f60f1fc9969d33080f3b905b08c63036bb99602d484b52530f6176242b224ed65444fd7cfc2df7d44f0b0dd039ac40
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/documentsearch@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/documentsearch@npm:4.0.5"
@@ -2562,6 +2708,24 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/nbformat@npm:^4.1.2":
+  version: 4.1.2
+  resolution: "@jupyterlab/nbformat@npm:4.1.2"
+  dependencies:
+    "@lumino/coreutils": ^2.1.2
+  checksum: 6c55337b667dcc5a6282f93972a30d227ba7c3f576fc4b60069408dd114dff1bc9f743bb6f984da088dfda25b7c4f25f13a472cd5c05b24af2e32b6b17172c6b
+  languageName: node
+  linkType: hard
+
+"@jupyterlab/nbformat@npm:^4.1.5":
+  version: 4.1.5
+  resolution: "@jupyterlab/nbformat@npm:4.1.5"
+  dependencies:
+    "@lumino/coreutils": ^2.1.2
+  checksum: d417d7eade40d389fea8593358b6455158cf3e67fa40c0c4c05c865852520acc466102109723c9cb16eecf95952617d79f7fe6be9da6ca3f601749bdecdfda97
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/notebook@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/notebook@npm:4.0.5"
@@ -2611,6 +2775,19 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/observables@npm:^5.1.2":
+  version: 5.1.2
+  resolution: "@jupyterlab/observables@npm:5.1.2"
+  dependencies:
+    "@lumino/algorithm": ^2.0.1
+    "@lumino/coreutils": ^2.1.2
+    "@lumino/disposable": ^2.1.2
+    "@lumino/messaging": ^2.0.1
+    "@lumino/signaling": ^2.1.2
+  checksum: 5bf7ec19c02d7d1923f4bf4c048f182957332a4e1f5481af980f976d518fd1590034cd529d7a980c228586b1650a796361a18b38b00bf6465ac0967ba6cdc8c0
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/outputarea@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/outputarea@npm:4.0.5"
@@ -2643,6 +2820,16 @@ __metadata:
   languageName: node
   linkType: hard
 
+"@jupyterlab/rendermime-interfaces@npm:^3.9.2":
+  version: 3.9.2
+  resolution: "@jupyterlab/rendermime-interfaces@npm:3.9.2"
+  dependencies:
+    "@lumino/coreutils": ^1.11.0 || ^2.1.2
+    "@lumino/widgets": ^1.37.2 || ^2.3.1
+  checksum: 65d6d4fe8c241b9f1267058db43a8fca01ee9fb6a67a267826accfdd0a9e71f2143fcad778b5c6d8b5bf825440ee9b040088253866e8e1a840b7276fba266b88
+  languageName: node
+  linkType: hard
+
 "@jupyterlab/rendermime@npm:^4.0.5":
   version: 4.0.5
   resolution: "@jupyterlab/rendermime@npm:4.0.5"
@@ -2663,22 +2850,42 @@ __metadata:
   languageName: node
   linkType: hard
 
-"@jupyterlab/services@npm:^7.0.5":
-  version: 7.0.5
-  resolution: "@jupyterlab/services@npm:7.0.5"
+"@jupyterlab/rendermime@npm:^4.1.2":
+  version: 4.1.2
+  resolution: "@jupyterlab/rendermime@npm:4.1.2"
+  dependencies:
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