anchor.diff:  part of Tabasci;
   
   typedef void DragCallback(DragHandler dragHandler, Element element, MouseEvent event);
  +// type of a function that determines if a drag should be allowed to start
  +typedef bool AllowDragStart(MouseEvent event);
   
   // TODO this should probably be a singleton. when do you drag more than one thing at a time?
   // TODO make universal enable/disable flag
  
positive.code:   }
    
    void _mouseDownHandler(MouseEvent event) {
      //print("mouse down, enabled: $enabled");
      // TODO if(!_dragging)?
      
  
negative.code:   
    /// Add a target to the set
    void addTarget(Element element) {
      print("adding target");
      // save size to compare with size after
      int oldSize = _targets.length;
      // add element
  