anchor.diff:  
     Function onFrame;
   
  -  List<sky.EventListener> eventListeners = new List<sky.EventListener>();
  +  final List<EventListener> _eventListeners = new List<EventListener>();
  +  void addEventListener(EventListener e) => _eventListeners.add(e);
  +  void removeEventListener(EventListener e) => _eventListeners.remove(e);
   
     RenderBox get root => _renderView.child;
     void set root(RenderBox value) {
  
positive.code: 
    PointerState({ this.result, this.lastPosition });
  }
  
  class AppView {
  
  
negative.code:       _renderView.hitTest(result, position: new Point(event.x, event.y));
        dispatchEvent(event, result);
      } else {
        for (EventListener e in _eventListeners) {
          e(event);
        }
      }
    }
  