anchor.diff:  
   final List<UINode> _emptyList = new List<UINode>();
   
  -abstract class OneChildListRenderObjectWrapper extends RenderObjectWrapper {
  -
  -  // In OneChildListRenderObjectWrapper subclasses, slots are RenderObject nodes
  +abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
  +
  +  // In MultiChildRenderObjectWrapper subclasses, slots are RenderObject nodes
     // to use as the "insert before" sibling in ContainerRenderObjectMixin.add() calls
   
     final List<UINode> children;
   
  -  OneChildListRenderObjectWrapper({
  +  MultiChildRenderObjectWrapper({
       Object key,
       List<UINode> children
     }) : this.children = children == null ? _emptyList : children,
  
positive.code:   }
  }
  
  class BlockContainer extends OneChildListRenderObjectWrapper {
    RenderBlock root;
    RenderBlock createNode() => new RenderBlock();
  
  
negative.code:     return false;
    }
  
    void syncRenderObject(MultiChildRenderObjectWrapper old) {
      super.syncRenderObject(old);
  
      if (root is! ContainerRenderObjectMixin)
  