anchor.diff:    bool get _isBuilding => _currentlyBuilding == this;
     bool _dirty = true;
   
  +  sky.Node get _host => _root.parentNode;
  +  sky.Node get _insertionPoint => _root == null ? _root : _root.nextSibling;
  +
     Node _built;
     final int _order;
     static int _currentOrder = 0;
  
positive.code:     if (!_dirty || _defunct)
        return;
  
      assert(_root != null);
      _sync(null, _root.parentNode, _root.nextSibling);
    }
  
    void scheduleBuild() {
  
negative.code: }
  
  abstract class App extends Component {
    sky.Node _host;
  
    App() : super(stateful: true) {
      _host = sky.document.createElement('div');
      sky.document.appendChild(_host);
      _scheduleComponentForRender(this);
    }
  }
  