anchor.diff:    bool canUpdateTo(View other) => (other is Elt) && other.name == name;
   
     void refresh(Elt nextVersion) {
  +    print("refresh Elt: ${_path}");
  +
       if (nextVersion == null) {
         return; // no internal state to update
       }
  
positive.code: 
    void refresh(Widget nextVersion) {
      assert(_mounted);
  
      if (_nextState != null) {
        _state = _nextState;
  
negative.code: 
      Element before = querySelector("[data-path=\"${_path}\"]");
  
      View newShadow = render();
      if (shadow.canUpdateTo(newShadow)) {
        shadow.refresh(newShadow);
      } else {
        shadow.unmount();
        shadow = newShadow;
        StringBuffer out = new StringBuffer();
        shadow.mount(out, _path, _depth);
        Element after = _unsafeNewElement(out.toString());
        before.replaceWith(after);
      }
    }
  
    Map<Symbol, dynamic> get props => _props;
  