docs: def get_child_story(self):
          logger.debug('# get_child_story')
          """
          try child story that match message and get scope of it
          :return:
          """
          story_loop = self.compiled_story()
          if hasattr(story_loop, 'children_matcher') and not self.matched:
              return self.get_story_scope_child(story_loop)
  
          story_part = self.get_current_story_part()
  
          if not hasattr(story_part, 'get_child_by_validation_result'):
              logger.debug('# does not have get_child_by_validation_result')
              return None
  
          if isinstance(self.waiting_for, forking.SwitchOnValue):
              logger.debug('# switch on value')
              return story_part.get_child_by_validation_result(self.waiting_for.value)
  
          # for some base classes we could try validate result direct
          child_story = story_part.get_child_by_validation_result(self.waiting_for)
          if child_story:
              logger.debug('# child_story')
              logger.debug(child_story)
              return child_story
  
          stack_tail = self.stack_tail()
          if stack_tail['data'] is not None and not self.matched:
              validator = matchers.deserialize(stack_tail['data'])
              logger.debug('# validator')
              logger.debug(validator)
              logger.debug('# self.message')
              logger.debug(self.message)
              validation_result = validator.validate(self.message)
              logger.debug('# validation_result')
              logger.debug(validation_result)
              res = story_part.get_child_by_validation_result(validation_result)
              logger.debug('# res')
              logger.debug(res)
              # or we validate message
              # but can't find right child story
              # maybe we should use independent validators for each story here
              if res is None:
                  return self.get_story_scope_child(story_part)
              else:
                  return res
  
          return None