diff --git a/src/vs/editor/contrib/snippet/browser/snippetVariables.ts b/src/vs/editor/contrib/snippet/browser/snippetVariables.ts
index 09c08f4b026ad7..96aebfb834d88e 100644
--- a/src/vs/editor/contrib/snippet/browser/snippetVariables.ts
+++ b/src/vs/editor/contrib/snippet/browser/snippetVariables.ts
@@ -41,6 +41,8 @@ export const KnownSnippetVariableNames: { [key: string]: true } = Object.freeze(
 	'TM_FILENAME_BASE': true,
 	'TM_DIRECTORY': true,
 	'TM_FILEPATH': true,
+	'CURSOR_INDEX': true, // 0-offset
+	'CURSOR_NUMBER': true, // 1-offset
 	'RELATIVE_FILEPATH': true,
 	'BLOCK_COMMENT_START': true,
 	'BLOCK_COMMENT_END': true,
@@ -140,6 +142,12 @@ export class SelectionBasedVariableResolver implements VariableResolver {
 
 		} else if (name === 'TM_LINE_NUMBER') {
 			return String(this._selection.positionLineNumber);
+
+		} else if (name === 'CURSOR_INDEX') {
+			return String(this._selectionIdx);
+
+		} else if (name === 'CURSOR_NUMBER') {
+			return String(this._selectionIdx + 1);
 		}
 		return undefined;
 	}
diff --git a/src/vs/editor/contrib/snippet/test/browser/snippetVariables.test.ts b/src/vs/editor/contrib/snippet/test/browser/snippetVariables.test.ts
index cfee631930bb68..fc53766a32e67c 100644
--- a/src/vs/editor/contrib/snippet/test/browser/snippetVariables.test.ts
+++ b/src/vs/editor/contrib/snippet/test/browser/snippetVariables.test.ts
@@ -118,6 +118,12 @@ suite('Snippet Variables Resolver', function () {
 		assertVariableResolve(resolver, 'TM_CURRENT_LINE', 'this is line two');
 		assertVariableResolve(resolver, 'TM_LINE_INDEX', '1');
 		assertVariableResolve(resolver, 'TM_LINE_NUMBER', '2');
+		assertVariableResolve(resolver, 'CURSOR_INDEX', '0');
+		assertVariableResolve(resolver, 'CURSOR_NUMBER', '1');
+
+		resolver = new SelectionBasedVariableResolver(model, new Selection(1, 2, 2, 3), 4, undefined);
+		assertVariableResolve(resolver, 'CURSOR_INDEX', '4');
+		assertVariableResolve(resolver, 'CURSOR_NUMBER', '5');
 
 		resolver = new SelectionBasedVariableResolver(model, new Selection(2, 3, 1, 2), 0, undefined);
 		assertVariableResolve(resolver, 'TM_SELECTED_TEXT', 'his is line one\nth');
diff --git a/src/vs/workbench/api/common/extHostNotebookDocuments.ts b/src/vs/workbench/api/common/extHostNotebookDocuments.ts
index 50995c9f93f1ec..fbb400ec64d990 100644
--- a/src/vs/workbench/api/common/extHostNotebookDocuments.ts
+++ b/src/vs/workbench/api/common/extHostNotebookDocuments.ts
@@ -4,7 +4,6 @@
  *--------------------------------------------------------------------------------------------*/
 
 import { Emitter } from 'vs/base/common/event';
-import { deepFreeze } from 'vs/base/common/objects';
 import { URI, UriComponents } from 'vs/base/common/uri';
 import { ILogService } from 'vs/platform/log/common/log';
 import * as extHostProtocol from 'vs/workbench/api/common/extHost.protocol';
@@ -32,7 +31,7 @@ export class ExtHostNotebookDocuments implements extHostProtocol.ExtHostNotebook
 	$acceptModelChanged(uri: UriComponents, event: SerializableObjectWithBuffers<extHostProtocol.NotebookCellsChangedEventDto>, isDirty: boolean, newMetadata?: NotebookDocumentMetadata): void {
 		const document = this._notebooksAndEditors.getNotebookDocument(URI.revive(uri));
 		const e = document.acceptModelChanged(event.value, isDirty, newMetadata);
-		this._onDidChangeNotebookDocument.fire(deepFreeze(e));
+		this._onDidChangeNotebookDocument.fire(e);
 	}
 
 	$acceptDirtyStateChanged(uri: UriComponents, isDirty: boolean): void {
diff --git a/src/vs/workbench/contrib/comments/browser/commentsEditorContribution.ts b/src/vs/workbench/contrib/comments/browser/commentsEditorContribution.ts
index aadf040bcb46e5..a5d5d56e14efa0 100644
--- a/src/vs/workbench/contrib/comments/browser/commentsEditorContribution.ts
+++ b/src/vs/workbench/contrib/comments/browser/commentsEditorContribution.ts
@@ -16,7 +16,7 @@ import { EditorAction, registerEditorAction, registerEditorContribution } from '
 import { ICodeEditorService } from 'vs/editor/browser/services/codeEditorService';
 import { IRange, Range } from 'vs/editor/common/core/range';
 import { IEditorContribution, IModelChangedEvent } from 'vs/editor/common/editorCommon';
-import { IModelDecorationOptions } from 'vs/editor/common/model';
+import { IModelDecorationOptions, IModelDeltaDecoration } from 'vs/editor/common/model';
 import { ModelDecorationOptions } from 'vs/editor/common/model/textModel';
 import * as languages from 'vs/editor/common/languages';
 import { peekViewResultsBackground, peekViewResultsSelectionBackground, peekViewTitleBackground } from 'vs/editor/contrib/peekView/browser/peekView';
@@ -61,25 +61,29 @@ export class ReviewViewZone implements IViewZone {
 	}
 }
 
-class CommentingRangeDecoration {
-	private _decorationId: string;
+class CommentingRangeDecoration implements IModelDeltaDecoration {
+	private _decorationId: string | undefined;
+	private _startLineNumber: number;
+	private _endLineNumber: number;
 
-	public get id(): string {
+	public get id(): string | undefined {
 		return this._decorationId;
 	}
 
-	constructor(private _editor: ICodeEditor, private _ownerId: string, private _extensionId: string | undefined, private _label: string | undefined, private _range: IRange, commentingOptions: ModelDecorationOptions, private commentingRangesInfo: languages.CommentingRanges, public readonly isHover: boolean = false) {
-		const startLineNumber = _range.startLineNumber;
-		const endLineNumber = _range.endLineNumber;
-		let commentingRangeDecorations = [{
-			range: {
-				startLineNumber: startLineNumber, startColumn: 1,
-				endLineNumber: endLineNumber, endColumn: 1
-			},
-			options: commentingOptions
-		}];
+	public set id(id: string | undefined) {
+		this._decorationId = id;
+	}
+
+	public get range(): IRange {
+		return {
+			startLineNumber: this._startLineNumber, startColumn: 1,
+			endLineNumber: this._endLineNumber, endColumn: 1
+		};
+	}
 
-		this._decorationId = this._editor.deltaDecorations([], commentingRangeDecorations)[0];
+	constructor(private _editor: ICodeEditor, private _ownerId: string, private _extensionId: string | undefined, private _label: string | undefined, private _range: IRange, public readonly options: ModelDecorationOptions, private commentingRangesInfo: languages.CommentingRanges, public readonly isHover: boolean = false) {
+		this._startLineNumber = _range.startLineNumber;
+		this._endLineNumber = _range.endLineNumber;
 	}
 
 	public getCommentAction(): { ownerId: string; extensionId: string | undefined; label: string | undefined; commentingRangesInfo: languages.CommentingRanges } {
@@ -96,7 +100,7 @@ class CommentingRangeDecoration {
 	}
 
 	public getActiveRange() {
-		return this._editor.getModel()!.getDecorationRange(this._decorationId);
+		return this.id ? this._editor.getModel()!.getDecorationRange(this.id) : undefined;
 	}
 }
 class CommentingRangeDecorator {
@@ -104,6 +108,7 @@ class CommentingRangeDecorator {
 	private decorationOptions!: ModelDecorationOptions;
 	private hoverDecorationOptions!: ModelDecorationOptions;
 	private commentingRangeDecorations: CommentingRangeDecoration[] = [];
+	private decorationIds: string[] = [];
 	private _editor: ICodeEditor | undefined;
 	private _infos: ICommentInfo[] | undefined;
 	private _lastHover: number = -1;
@@ -163,8 +168,8 @@ class CommentingRangeDecorator {
 			});
 		}
 
-		let oldDecorations = this.commentingRangeDecorations.map(decoration => decoration.id);
-		editor.deltaDecorations(oldDecorations, []);
+		this.decorationIds = editor.deltaDecorations(this.decorationIds, commentingRangeDecorations);
+		commentingRangeDecorations.forEach((decoration, index) => decoration.id = this.decorationIds[index]);
 
 		const rangesDifference = this.commentingRangeDecorations.length - commentingRangeDecorations.length;
 		this.commentingRangeDecorations = commentingRangeDecorations;