docs: def get_persistent_items(self):
          """
          Returns attached container items and container configurations that are marked as persistent. Each returned
          item is in the format ``(config name, instance/attached name)``, where the instance name can also be ``None``.
  
          :return: Lists of attached items.
          :rtype: (list[(unicode | str, unicode | str)], list[unicode | str, unicode | str | NoneType])
          """
          attached_items = [(container, ac)
                            for container, config in self
                            for ac in config.attaches]
          persistent_containers = [(container, ci)
                                   for container, config in self if config.persistent
                                   for ci in config.instances or [None]]
          return attached_items, persistent_containers