anchor.diff:        return;
   
       assert(_host != null);
  +    _trace('$_key rebuilding...');
       _sync(null, _host, _insertionPoint);
     }
   
  
positive.code:   }
  
    void _remove() {
      content._remove();
      super._remove();
    }
  }
  
negative.code:   void _remove() {
      assert(_built != null);
      assert(_root != null);
      _removeChild(_built);
      _built = null;
      _unmountedComponents.add(this);
      super._remove();
  