anchor.diff:    final CanvasElement _canvas;
     final Stage _stage;
     final AffineTransform _tx;
  -  final Dragger _dragger;
     final _DemoValue _demoMapper;
   
     Coordinate _mouseLocation;
     bool _frameRequested = false;
  -  bool _overShape = false;
  +  final Thing _thing;
   
     factory DraggerDemo(CanvasElement canvas){
   
  
positive.code:     final arrayValue = [_tx.translateX, _tx.translateY];
      _demoMapper.input = arrayValue;
      requestFrame();
    }
  
    void _onDragStart(CancelableEventArgs e) {
      if(!_overShape) {
        e.cancel();
      }
    }
  
    void _onFrame(double highResTime){
  
negative.code:     _frameRequested = false;
      requestFrame();
    }
  }
  
  class _DemoValue extends SendPortValue<List<int>, int> {
  