docs: def _check_transition_validity(self, check_transition):
          """Checks the validity of a transition
  
          Calls further checks to inspect the id, origin, target and connection of the transition.
  
          :param rafcon.core.transition.Transition check_transition: The transition to be checked
          :return bool validity, str message: validity is True, when the transition is valid, False else. message gives
              more information especially if the transition is not valid
          """
          valid, message = self._check_transition_id(check_transition)
          if not valid:
              return False, message
  
          # Separate check for start transitions
          if check_transition.from_state is None:
              return self._check_start_transition(check_transition)
  
          valid, message = self._check_transition_origin(check_transition)
          if not valid:
              return False, message
  
          valid, message = self._check_transition_target(check_transition)
          if not valid:
              return False, message
  
          return self._check_transition_connection(check_transition)