anchor.diff:    }
   
     void invalidateDraw(){
  -    _invalidateParent();
  +    if(_lastDrawSize != null){
  +      _lastDrawSize = null;
  +      _invalidateParent();
  +    }
     }
   
     bool hasVisualChild(PElement element){
  
positive.code:   final List<AffineTransform> _transforms;
    final HashMap<Property, Object> propertyValues;
    final bool cacheEnabled;
    num width, height, _alpha;
    Size _lastDrawSize;
    bool clip = false;
    IElementParent _parent;
  
    PElement(int this.width, int this.height, [bool this.cacheEnabled = false]) :
      _transforms = new List<AffineTransform>(),
      propertyValues = new HashMap<Property, Object>()
    {
  
negative.code:   }
  
    void _invalidateParent(){
      assert(this._parent != null);
      _parent.childInvalidated(this);
    }
  }
  