anchor.diff:      } else {
         _traceSync(_SyncOperation.STATELESS, node._key);
       }
  -    node._sync(oldNode, host, insertBefore);
  +    node._sync(oldNode, slot);
       if (oldNode != null)
         oldNode._defunct = true;
   
  
positive.code:       return;
  
      _trace('$_key rebuilding...');
      _sync(null, _host, _root);
    }
  }
  
  
negative.code:   static Component _currentlyBuilding;
    List<Function> _mountCallbacks;
    List<Function> _unmountCallbacks;
    dynamic _slot; // cached slot from the last time we were synced
  
    void onDidMount(Function fn) {
      if (_mountCallbacks == null)
  