anchor.diff:    num _width, _height, _alpha = 1;
     bool _cacheEnabled = false;
     Size _lastDrawSize;
  -  bool clip = false;
     ThingParent _parent;
   
     Thing(this._width, this._height);
  
positive.code:     drawOverride(ctx);
    }
  
    bool _isClipped(AffineTransform tx, CanvasRenderingContext2D ctx){
      if(clip){
        // a lot more impl to do here...
      }
      return false;
    }
  
    void _invalidateParent(){
      assert(this._parent != null);
      _invalidatedEventHandle.fireEvent(EventArgs.empty);
  
negative.code: 
  // TODO: 'alpha' does not compose well. If a parent is 50% and the child is
  //       50% the render should be at %25, right? :-/
  // TODO: support clipping - https://github.com/kevmoo/bot.dart/issues/15
  
  abstract class Thing extends AttachableObject {
    final List<AffineTransform> _transforms = new List<AffineTransform>();
  