anchor.diff:  
     StreamSubscription<MouseEvent> mouseMoveStream;
     StreamSubscription<MouseEvent> mouseUpStream;
  -  StreamSubscription<KeyboardEvent> keydownStream;
  +  StreamSubscription<KeyboardEvent> keydownStream, keyupStream;
   
     EventEmitterEvent changeEvent;
   
  
positive.code:     //this.domElement.addEventListener( 'DOMMouseScroll', mousewheel, false ); // firefox
  
      keydownStream = window.onKeyDown.listen(keydown);
      window.onKeyUp.listen(keyup);
  
  
      handleResize();
  
negative.code:       }
  
      }
  
      void unlisten() {
        keydownStream.cancel();
        keyupStream.cancel();
      }
  }
  