docs: def modify_target(self, to_state, to_outcome=None):
          """Set both to_state and to_outcome at the same time to modify transition target
  
          :param str to_state: State id of the target state
          :param int to_outcome: Outcome id of the target port
          :raises exceptions.ValueError: If parameters have wrong types or the new transition is not valid
          """
          if not (to_state is None and (to_outcome is not int and to_outcome is not None)):
              if not isinstance(to_state, string_types):
                  raise ValueError("Invalid transition target port: to_state must be a string")
              if not isinstance(to_outcome, int) and to_outcome is not None:
                  raise ValueError("Invalid transition target port: to_outcome must be of type int or None (if to_state "
                                   "is of type str)")
  
          old_to_state = self.to_state
          old_to_outcome = self.to_outcome
          self._to_state = to_state
          self._to_outcome = to_outcome
  
          valid, message = self._check_validity()
          if not valid:
              self._to_state = old_to_state
              self._to_outcome = old_to_outcome
              raise ValueError("The transition target could not be changed: {0}".format(message))