anchor.diff:    String get _tagName => 'div';
   
     static final Container _emptyContainer = new Container();
  -  Element get _emptyElement => _emptyContainer;
  +
  +  Node get _emptyNode => _emptyContainer;
   
     Container({
       Object key,
  
positive.code: }
  
  abstract class Node {
    String _key = null;
    sky.Node _root = null;
  
    // TODO(abarth): Both Elements and Components have |events| but |Text|
    // doesn't. Should we add a common base class to contain |events|?
  
negative.code:     }
  
      assert(vdom._root != null);
      _syncInternal();
    }
  
    void setState(Function fn()) {
      assert(_vdom != null || _defunct); // cannot setState before mounting.
      _stateful = true;
      fn();
      if (!_defunct && _currentlyRendering != this) {
        _dirty = true;
        _scheduleComponentForRender(this);
      }
  