docs: def add_separator(self, sub_menu='Advanced'):
          """
          Adds a sepqrator to the editor's context menu.
  
          :return: The sepator that has been added.
          :rtype: QtWidgets.QAction
          """
          action = QtWidgets.QAction(self)
          action.setSeparator(True)
          if sub_menu:
              try:
                  mnu = self._sub_menus[sub_menu]
              except KeyError:
                  pass
              else:
                  mnu.addAction(action)
          else:
              self._actions.append(action)
          return action