anchor.diff:  
     BoxConstraints _additionalConstraints;
     BoxConstraints get additionalConstraints => _additionalConstraints;
  -  void set additionalConstraints (BoxConstraints value) {
  -    assert(value != null);
  -    if (_additionalConstraints == value)
  -      return;
  -    _additionalConstraints = value;
  +  void set additionalConstraints (BoxConstraints newConstraints) {
  +    assert(newConstraints != null);
  +    if (_additionalConstraints == newConstraints)
  +      return;
  +    _additionalConstraints = newConstraints;
       markNeedsLayout();
     }
   
  
positive.code: 
    double _opacity;
    double get opacity => _opacity;
    void set opacity (double value) {
      assert(value != null);
      assert(value >= 0.0 && value <= 1.0);
      if (_opacity == value)
        return;
      _opacity = value;
      markNeedsPaint();
    }
  
  
negative.code: 
    Color _color;
    Color get color => _color;
    void set color (Color newColor) {
      assert(newColor != null);
      if (_color == newColor)
        return;
      _color = newColor;
      markNeedsPaint();
    }
  
    sky.TransferMode _transferMode;
    sky.TransferMode get transferMode => _transferMode;
    void set transferMode (sky.TransferMode newTransferMode) {
      assert(newTransferMode != null);
      if (_transferMode == newTransferMode)
        return;
      _transferMode = newTransferMode;
      markNeedsPaint();
    }
  
  