anchor.diff:      _disabled = value;
       _element.toggleClass(disabledClassName, value);
     }
  +
  +  set hidden(bool value) {
  +    _element.toggleAttr('hidden', value);
  +  }
   }
   
   class Octicon {
  
positive.code:   DisableableButton showHintButton;
  
    DElement navBarElement;
    TabController tabController;
    TabView editorTabView;
    TabView testTabView;
    TabView solutionTabView;
  
negative.code: 
      super.selectTab(tabName);
    }
  
    void setTabVisibility(String tabName, bool visible) {
      TabElement tab = tabs.firstWhere((t) => t.name == tabName);
      tab.toggleAttr('hidden', !visible);
    }
  }
  
  /// A container underneath the tab strip that can show or hide itself as needed.
  