code: public CmsMenuItemVisibilityMode addMessageKey(String messageKey) {
  
          CmsMenuItemVisibilityMode mode = clone();
          mode.m_messageKey = messageKey;
          return mode;
      }
docs: Adds the name of the message key for the visibility mode.<p>
  
  @param messageKey the name of the message key for the visibility mode
  @return an extended visibility mode containing the message key