anchor.diff:  
     // The source text retrieved during the previous update.
     String _sourceTextAtLastUpdate = null;
  +
  +  // Message displayed if the user has modified the document.
  +  static final String _UNLOAD_CONFIRMATION_MESSAGE = '''
  +If you leave this page, all data you have entered on this page will be lost.
  +
  +Please make sure to save any data you would like to keep by copying it from this
  +page and saving it on your computer.
  +''';
   }
   
   
  
positive.code:   void _onSourceTextChange(JsObject e, JsObject t) {
      _updateTimer.cancel();
      _updateTimer = new Timer(_UPDATE_DELAY, _update);
    }
  
    // Logger.
  
negative.code:     builder.allowNavigation(new _AllowAllUriPolicy());
      builder.allowImages(new _AllowAllUriPolicy());
      _outputNodeValidator = builder;
  
      // Set up onload confirmation dialog.
      window.onBeforeUnload.listen(_onBeforeUnload);
    }
  
    // Loads a document into the editor view.
  