anchor.diff:            break;
         }
   
  +      dispatchEvent(startEvent);
       }
   
       touchmove( TouchEvent event ) {
  
positive.code:       mouseMoveStream.cancel();
        mouseUpStream.cancel();
  
      }
  
      mousewheel( WheelEvent event ) {
  
negative.code:     _panEnd = new Vector2.zero();
  
      changeEvent = new EventEmitterEvent(type: 'change');
      startEvent = new EventEmitterEvent(type: 'start');
      endEvent = new EventEmitterEvent(type: 'end');
  
      this.domElement
      ..onContextMenu.listen(( event ) => event.preventDefault())
  