anchor.diff:    }
   }
   
  -/// Base class for instantiations of widgets that have builders and can be
  -/// marked dirty.
  +/// An [Element] that can be marked dirty and rebuilt.
   abstract class BuildableElement extends Element {
  +  /// Creates an element that instantiates the given widget.
     BuildableElement(Widget widget) : super(widget);
   
     /// Returns true if the element has been marked as needing rebuilding.
  
positive.code: ///
  /// Inherited widgets, when referenced in this way, will cause the consumer to
  /// rebuild when the inherited widget itself changes state.
  abstract class InheritedWidget extends _ProxyWidget {
    const InheritedWidget({ Key key, Widget child })
      : super(key: key, child: child);
  
  
negative.code: /// Elements can, in principle, have children. Only subclasses of
  /// RenderObjectElement are allowed to have more than one child.
  abstract class Element implements BuildContext {
    /// Creates an element that instantiates the given widget.
    Element(Widget widget) : _widget = widget {
      assert(widget != null);
    }
  