code: func (s *TasksCancelService) ParentTaskId(parentTaskId string) *TasksCancelService {
  	s.parentTaskId = parentTaskId
  	return s
  }
docs: // ParentTaskId specifies to cancel tasks with specified parent task id.
  // Notice that the caller is responsible for using the correct format,
  // i.e. node_id:task_number, as specified in the REST API.