src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts/MainThreadLanguageFeatures/$registerDocumentFormattingSupport
class MainThreadLanguageFeatures:	$registerDocumentFormattingSupport(handle: number, selector: IDocumentFilterDto[], extensionId: ExtensionIdentifier, displayName: string): void {
		this._registrations.set(handle, modes.DocumentFormattingEditProviderRegistry.register(selector, <modes.DocumentFormattingEditProvider>{
			extensionId,
			displayName,
			provideDocumentFormattingEdits: (model: ITextModel, options: modes.FormattingOptions, token: CancellationToken): Promise<ISingleEditOperation[] | undefined> => {
				return this._proxy.$provideDocumentFormattingEdits(handle, model.uri, options, token);
			}
		}));
	}