docs: def add_action(self, action, sub_menu='Advanced'):
          """
          Adds an action to the editor's context menu.
  
          :param action: QAction to add to the context menu.
          :param sub_menu: The name of a sub menu where to put the action.
              'Advanced' by default. If None or empty, the action will be added
              at the root of the submenu.
          """
          if sub_menu:
              try:
                  mnu = self._sub_menus[sub_menu]
              except KeyError:
                  mnu = QtWidgets.QMenu(sub_menu)
                  self.add_menu(mnu)
                  self._sub_menus[sub_menu] = mnu
              finally:
                  mnu.addAction(action)
          else:
              self._actions.append(action)
          action.setShortcutContext(QtCore.Qt.WidgetShortcut)
          self.addAction(action)