anchor.diff:    HtmlElement get _targetElement =>
         target == null ? null : querySelector(target);
     CssStyleDeclaration _originalStyle;
  +  Timer _transitionEndTimer;
   
     FoldButtonElement.created() : super.created();
   
  
positive.code:     } else {
        _restoreStyles(t.style);
      }
    }
  
    _saveStyles(CssStyleDeclaration style) =>
        PROP_NAMES.forEach((p) => _saveStyle(style, p));
    _saveStyle(CssStyleDeclaration style, String propName) {
  
negative.code:   attached() {
      super.attached();
      onClick.listen((_) => toggle());
    }
  
    void toggle() { folding = !folding; }
  