anchor.diff:        return;
   
       assert(_host != null);
  +    _trace('$_key rebuilding...');
       _sync(null, _host, _insertionPoint);
     }
   
  
positive.code:     super._remove();
      if (_children != null) {
        for (var child in _children) {
          child._remove();
        }
      }
    }
  
negative.code:     currentNode = null;
      while (oldStartIndex < oldEndIndex) {
        oldNode = oldChildren[oldStartIndex];
        _removeChild(oldNode);
        advanceOldStartIndex();
      }
    }
  