docs: public void disableTab(E tabContent, String reason) {
  
          Integer index = new Integer(m_tabPanel.getWidgetIndex(tabContent));
          Element tab = getTabElement(index.intValue());
          if ((tab != null) && !m_disabledTabIndexes.containsKey(index)) {
              if (CmsStringUtil.isNotEmptyOrWhitespaceOnly(tab.getTitle())) {
                  m_disabledTabIndexes.put(index, tab.getTitle());
              } else {
                  m_disabledTabIndexes.put(index, "");
              }
              tab.addClassName(I_CmsLayoutBundle.INSTANCE.tabbedPanelCss().tabDisabled());
              tab.setTitle(reason);
          }
      }