code: def iterate_fs(self):
          # type: () -> Iterator[Tuple[Text, FS]]
          
          if self._fs_sequence is None:
              self._fs_sequence = [
                  (name, fs)
                  for name, (_order, fs) in sorted(
                      self._filesystems.items(), key=itemgetter(1), reverse=True
                  )
              ]
          return iter(self._fs_sequence)
docs: Get iterator that returns (name, fs) in priority order.