anchor.diff:    external void alert(String msg);
     external Menu createMenu(String caption);
     external Menu createAddonMenu();
  +  external void showModalDialog(HtmlOutput userInterface, String title);
  +  external void showSidebar(HtmlOutput userInterface);
   }
   
   @JS()
  
positive.code: class SpreadsheetApp {
    external static UI getUi();
    external static Spreadsheet getActiveSpreadsheet();
  }
  
  @JS()
  
negative.code: library hello;
  
  import 'package:js/js.dart';
  
  @JS()
  class HtmlService {
    // TODO: argument could also be a `BlobSource`. Don't need it yet.
    external static HtmlOutput createHtmlOutput([String html]);
  }
  
  @JS()
  class HtmlOutput {
    external HtmlOutput setContent(String content);
    external HtmlOutput setWidth(int width);
    external HtmlOutput setHeight(int height);
    external HtmlOutput setTitle(String title);
    external int getWidth();
    external int getHeight();
    external String getTitle();
  }
  
  @JS()
  class DocumentApp {
  