anchor.diff:      super.mount(parent, slot);
     }
   
  +  void _notifyChildren(Element child) {
  +    if (child is RenderObjectElement) {
  +      child._updateParentData(widget);
  +    } else {
  +      assert(child is! ParentDataElement<RenderObjectWidget>);
  +      child.visitChildren(_notifyChildren);
  +    }
  +  }
  +
     @override
     void notifyClients(ParentDataWidget<T> oldWidget) {
  -    void notifyChildren(Element child) {
  -      if (child is RenderObjectElement) {
  -        child._updateParentData(widget);
  -      } else {
  -        assert(child is! ParentDataElement<RenderObjectWidget>);
  -        child.visitChildren(notifyChildren);
  -      }
  -    }
  -    visitChildren(notifyChildren);
  -  }
  -}
  -
  -/// Base class for instantiations of [InheritedWidget] subclasses.
  +    visitChildren(_notifyChildren);
  +  }
  +}
  +
  +/// An element that uses a [InheritedWidget] as its configuration.
   class InheritedElement extends ProxyElement {
  +  /// Creates an element that uses the given widget as its configuration.
     InheritedElement(InheritedWidget widget) : super(widget);
   
     @override
  
positive.code:   }
  }
  
  /// Instantiation of [RenderObjectWidget]s that can have a list of children.
  ///
  /// This element subclass can be used for RenderObjectWidgets whose
  /// RenderObjects use the [ContainerRenderObjectMixin] mixin with a parent data
  /// type that implements [ContainerParentDataMixin<RenderObject>]. Such widgets
  /// are expected to inherit from [MultiChildRenderObjectWidget].
  class MultiChildRenderObjectElement extends RenderObjectElement {
    MultiChildRenderObjectElement(MultiChildRenderObjectWidget widget) : super(widget) {
      assert(!debugChildrenHaveDuplicateKeys(widget, widget.children));
    }
  
negative.code: 
  /// An [Element] that can be marked dirty and rebuilt.
  abstract class BuildableElement extends Element {
    /// Creates an element that uses the given widget as its configuration.
    BuildableElement(Widget widget) : super(widget);
  
    /// Returns true if the element has been marked as needing rebuilding.
  