anchor.diff:  
   class Selector implements IMode {
       Hub _hub;
  +    bool isRunning;
   
  -    Shape _selectedShape;
       Shape _possibleShape;
  -    int _pickedId;
  -    bool isRunning;
  +    int _possibleId;
   
       Selector() {
           _hub = Hub.root;
  
positive.code:             return;
          }
  
          _selectedShape.isSelected = false;
  
          _selectedShape = _possibleShape;
          _selectedShape.isSelected = true;
          _possibleShape = null;
      }
  }
  
negative.code: 
          List l = _hub.picker.find(p);
          if (l == null) return;
  
          _possibleShape = l[0];
          _possibleId = l[1];
      }
  
      void _handleMouseUp(MouseData data) {
  