code: protected void toggleElementVisibility() {
  
          if (CmsDomUtil.hasClass(HIDE_ELEMENTS_CLASS, getGroupContainerWidget().getElement())) {
              getGroupContainerWidget().removeStyleName(HIDE_ELEMENTS_CLASS);
          } else {
              getGroupContainerWidget().addStyleName(HIDE_ELEMENTS_CLASS);
          }
          getGroupContainerWidget().refreshHighlighting();
      }
docs: Toggles the visibility of hidden elements.<p>