anchor.diff:      return false;
     }
   
  -  void syncRenderObject(OneChildListRenderObjectWrapper old) {
  +  void syncRenderObject(MultiChildRenderObjectWrapper old) {
       super.syncRenderObject(old);
   
       if (root is! ContainerRenderObjectMixin)
  
positive.code:     : super(key: key, children: children);
  }
  
  class StackContainer extends OneChildListRenderObjectWrapper {
    RenderStack root;
    RenderStack createNode() => new RenderStack();
  
  
negative.code:   }
  }
  
  class BlockContainer extends MultiChildRenderObjectWrapper {
    RenderBlock root;
    RenderBlock createNode() => new RenderBlock();
  
  