anchor.diff:  
     void _remove() {
       _defunct = true;
  -    _root = null;
  +    root = null;
       handleRemoved();
     }
     void handleRemoved() { }
  
positive.code:     return false;
    }
  
    void _syncRenderNode(OneChildListRenderNodeWrapper old) {
      super._syncRenderNode(old);
  
      if (_root is! RenderCSSContainer)
        return;
  
      var startIndex = 0;
  
negative.code:       return;
  
      _trace('$_key rebuilding...');
      assert(root != null);
      _sync(null, _slot);
    }
  
  