anchor.diff:    RenderCSS _createNode();
     RenderNodeWrapper get _emptyNode;
   
  -  void _sync(UINode old, RenderCSSContainer host, RenderCSS insertBefore) {
  +  void insert(RenderNodeWrapper child, dynamic slot);
  +
  +  void _sync(UINode old, dynamic slot) {
       if (old == null) {
         _root = _createNode();
         assert(_root != null);
  -      host.add(_root, before: insertBefore);
  +      var ancestor = findAncestor(RenderNodeWrapper);
  +      if (ancestor is RenderNodeWrapper)
  +        ancestor.insert(this, slot);
         old = _emptyNode;
       } else {
         _root = old._root;
  
positive.code:     handleRemoved();
    }
    void handleRemoved() { }
  
    int _nodeDepth;
    void _ensureDepth() {
  
negative.code: 
  abstract class OneChildListRenderNodeWrapper extends RenderNodeWrapper {
  
    // In OneChildListRenderNodeWrapper subclasses, slots are RenderCSS nodes
    // to use as the "insert before" sibling in RenderCSSContainer.add() calls
  
    final List<UINode> children;
  
    OneChildListRenderNodeWrapper({
  