diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/mappedEdits.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/mappedEdits.test.ts
index f4fc349f115..72413a2773f 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/mappedEdits.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/mappedEdits.test.ts
@@ -18,13 +18,12 @@ suite('mapped edits provider', () => {
 		const r1 = vscode.chat.registerMappedEditsProvider(tsDocFilter, {
 			provideMappedEdits: (_doc: vscode.TextDocument, codeBlocks: string[], context: vscode.MappedEditsContext, _token: vscode.CancellationToken) => {
 
-				assert(context.selections.length === 1);
-				assert(context.related.length === 1);
-				assert('uri' in context.related[0] && 'range' in context.related[0]);
+				assert((context as any).selections.length === 1); // context.selections is for backward compat
+				assert(context.documents.length === 1);
 
 				const edit = new vscode.WorkspaceEdit();
 				const text = codeBlocks.join('\n//----\n');
-				edit.replace(uri, context.selections[0], text);
+				edit.replace(uri, context.documents[0][0].ranges[0], text);
 				return edit;
 			}
 		});
@@ -37,12 +36,16 @@ suite('mapped edits provider', () => {
 				`function foo() {\n\treturn 1;\n}`,
 			],
 			{
-				selections: [new vscode.Selection(0, 0, 1, 0)],
-				related: [
-					{
-						uri,
-						range: new vscode.Range(new vscode.Position(0, 0), new vscode.Position(1, 0))
-					}
+				documents: [
+					[
+						{
+							uri,
+							version: 1,
+							ranges: [
+								new vscode.Range(new vscode.Position(0, 0), new vscode.Position(1, 0))
+							]
+						}
+					]
 				]
 			}
 		);
@@ -60,13 +63,9 @@ suite('mapped edits provider', () => {
 		const r1 = vscode.chat.registerMappedEditsProvider(tsDocFilter, {
 			provideMappedEdits: (_doc: vscode.TextDocument, codeBlocks: string[], context: vscode.MappedEditsContext, _token: vscode.CancellationToken) => {
 
-				assert(context.selections.length === 1);
-				assert(context.related.length === 1);
-				assert('uri' in context.related[0] && 'range' in context.related[0]);
-
 				const edit = new vscode.WorkspaceEdit();
 				const text = codeBlocks.join('\n//----\n');
-				edit.replace(uri, context.selections[0], text);
+				edit.replace(uri, context.documents[0][0].ranges[0], text);
 				return edit;
 			}
 		});
@@ -80,12 +79,16 @@ suite('mapped edits provider', () => {
 				`function foo() {\n\treturn 1;\n}`,
 			],
 			{
-				selections: [new vscode.Selection(0, 0, 1, 0)],
-				related: [
-					{
-						uri,
-						range: new vscode.Range(new vscode.Position(0, 0), new vscode.Position(1, 0))
-					}
+				documents: [
+					[
+						{
+							uri,
+							version: 1,
+							ranges: [
+								new vscode.Range(new vscode.Position(0, 0), new vscode.Position(1, 0))
+							]
+						}
+					]
 				]
 			}
 		);
diff --git a/src/vs/workbench/api/common/extHostCommands.ts b/src/vs/workbench/api/common/extHostCommands.ts
index fd3ba6c52b9..beb10dcddac 100644
--- a/src/vs/workbench/api/common/extHostCommands.ts
+++ b/src/vs/workbench/api/common/extHostCommands.ts
@@ -123,7 +123,7 @@ export class ExtHostCommands implements ExtHostCommandsShape {
 
 			const internalArgs = apiCommand.args.map((arg, i) => {
 				if (!arg.validate(apiArgs[i])) {
-					throw new Error(`Invalid argument '${arg.name}' when running '${apiCommand.id}', received: ${apiArgs[i]}`);
+					throw new Error(`Invalid argument '${arg.name}' when running '${apiCommand.id}', received: ${typeof apiArgs[i] === 'object' ? JSON.stringify(apiArgs[i], null, '\t') : apiArgs[i]} `);
 				}
 				return arg.convert(apiArgs[i]);
 			});
@@ -238,7 +238,7 @@ export class ExtHostCommands implements ExtHostCommandsShape {
 				try {
 					validateConstraint(args[i], description.args[i].constraint);
 				} catch (err) {
-					throw new Error(`Running the contributed command: '${id}' failed. Illegal argument '${description.args[i].name}' - ${description.args[i].description}`);
+					throw new Error(`Running the contributed command: '${id}' failed.Illegal argument '${description.args[i].name}' - ${description.args[i].description} `);
 				}
 			}
 		}
@@ -342,7 +342,7 @@ export const IExtHostCommands = createDecorator<IExtHostCommands>('IExtHostComma
 
 export class CommandsConverter implements extHostTypeConverter.Command.ICommandsConverter {
 
-	readonly delegatingCommandId: string = `__vsc${Date.now().toString(36)}`;
+	readonly delegatingCommandId: string = `__vsc${Date.now().toString(36)} `;
 	private readonly _cache = new Map<string, vscode.Command>();
 	private _cachIdPool = 0;
 
@@ -387,7 +387,7 @@ export class CommandsConverter implements extHostTypeConverter.Command.ICommands
 			// we have a contributed command with arguments. that
 			// means we don't want to send the arguments around
 
-			const id = `${command.command}/${++this._cachIdPool}`;
+			const id = `${command.command} /${++this._cachIdPool}`;
 			this._cache.set(id, command);
 			disposables.add(toDisposable(() => {
 				this._cache.delete(id);
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index b22d52ebead..9055980c1e4 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -1567,14 +1567,20 @@ export namespace LanguageSelector {
 export namespace MappedEditsContext {
 
 	export function is(v: unknown): v is vscode.MappedEditsContext {
-		return (!!v &&
-			typeof v === 'object' &&
-			'selections' in v &&
-			Array.isArray(v.selections) &&
-			v.selections.every(s => s instanceof types.Selection) &&
-			'related' in v &&
-			Array.isArray(v.related) &&
-			v.related.every(e => e && typeof e === 'object' && URI.isUri(e.uri) && e.range instanceof types.Range));
+		return (
+			!!v && typeof v === 'object' &&
+			'documents' in v &&
+			Array.isArray(v.documents) &&
+			v.documents.every(subArr =>
+				Array.isArray(subArr) &&
+				subArr.every(docRef =>
+					docRef && typeof docRef === 'object' &&
+					'uri' in docRef && URI.isUri(docRef.uri) &&
+					'version' in docRef && typeof docRef.version === 'number' &&
+					'ranges' in docRef && Array.isArray(docRef.ranges) && docRef.ranges.every((r: unknown) => r instanceof types.Range)
+				)
+			)
+		);
 	}
 
 	export function from(extContext: vscode.MappedEditsContext): languages.MappedEditsContext {