docs: def _check_transition_validity(self, check_transition):
          """ Transition of BarrierConcurrencyStates must least fulfill the condition of a ContainerState.
          Start transitions are forbidden in the ConcurrencyState.
  
          :param check_transition: the transition to check for validity
          :return:
          """
          valid, message = super(BarrierConcurrencyState, self)._check_transition_validity(check_transition)
          if not valid:
              return False, message
  
          # Only the following transitions are allowed in barrier concurrency states:
          # - Transitions from the decider state to the parent state\n"
          # - Transitions from not-decider states to the decider state\n"
          # - Transitions from not_decider states from aborted/preempted outcomes to the
          #   aborted/preempted outcome of the parent
  
          from_state_id = check_transition.from_state
          to_state_id = check_transition.to_state
          from_outcome_id = check_transition.from_outcome
          to_outcome_id = check_transition.to_outcome
  
          if from_state_id == UNIQUE_DECIDER_STATE_ID:
              if to_state_id != self.state_id:
                  return False, "Transition from the decider state must go to the parent state"
          else:
              if to_state_id != UNIQUE_DECIDER_STATE_ID:
                  if from_outcome_id not in [-2, -1] or to_outcome_id not in [-2, -1]:
                      return False, "Transition from this state must go to the decider state. The only exception are " \
                                    "transition from aborted/preempted to the parent aborted/preempted outcomes"
  
          return True, message