anchor.diff:    }
   
     void cleanUpNode([bool cleanUp = true]) {
  +    //print("GroupingBehavior.cleanUpNode: $cleanUp --------------------------");
       if (_children != null && _children.isNotEmpty) {
         _children.forEach((BaseNode child) => child.cleanup(cleanUp));
         if (cleanUp)
  
positive.code:    * [tag] is an integer to identify the [Node] easily.
     */
    void addChild(BaseNode child, [int zOrder = 0, int tag = 0]) {
      if (child == this) {
        Logging.error("GroupingBehavior.addChild: A node can't be added as a child to itself.");
        return;
      }
  
negative.code:     if (child._parent != null) {
        // This node already has a parent which means it has been parented
        // to another node. This scenegraph is a DAG, hence no circular potentials.
        Logging.error(
          "GroupingBehavior.addChild: child:${child} is already parented to ${child._parent}."
          " {_this} node is ${_this},P:${_this._parent}.");
        return;
      }
  
  