docs: def _repeat(self, index, stage, stop):
          """ Repeat a stage.
  
          :param index: Stage index.
          :param stage: Stage object to repeat.
          :param iterations: Number of iterations (default infinite).
          :param stages: Stages back to repeat (default 1).
          """
          times = None
          if 'iterations' in stage.kwargs:
              times = stage.kwargs['iterations'] - 1
          stages_back = 1
          if 'stages' in stage.kwargs:
              stages_back = stage.kwargs['stages']
          i = 0
          while i != times:
              if stop.is_set():
                  break
              for forward in range(stages_back):
                  if stop.is_set():
                      break
                  stage_index = index - stages_back + forward
                  self._execute_stage(stage_index, self._pipe[stage_index], stop)
              i += 1