docs: def observe_root_state_assignments(self, model, prop_name, info):
          """ The method relieves observed root_state models and observes newly assigned root_state models.
          """
          if info['old']:
              self.relieve_model(info['old'])
          if info['new']:
              self.observe_model(info['new'])
              self.logger.info("Exchange observed old root_state model with newly assigned one. sm_id: {}"
                               "".format(info['new'].state.parent.state_machine_id))