anchor.diff:  
     bool get interchangeable => false; // if true, then keys can be duplicated
   
  -  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore);
  +  void _sync(UINode old, dynamic slot);
  +  // 'slot' is the identifier that the parent RenderNodeWrapper uses to know
  +  // where to put this descendant
   
     void _remove() {
       _defunct = true;
  
positive.code:     } else {
        _traceSync(_SyncOperation.STATELESS, node._key);
      }
      node._sync(oldNode, host, insertBefore);
      if (oldNode != null)
        oldNode._defunct = true;
  
  
negative.code: 
    ContentNode(UINode content) : this.content = content, super(key: content._key);
  
    void _sync(UINode old, dynamic slot) {
      UINode oldContent = old == null ? null : (old as ContentNode).content;
      content = _syncChild(content, oldContent, slot);
      assert(content._root != null);
      _root = content._root;
    }
  