docs: def started_tasks(self, task_registry_id=None, task_cls=None):
  		""" Return tasks that was started. Result way be filtered by the given arguments.
  
  		:param task_registry_id: if it is specified, then try to return single task which id is the same as \
  		this value.
  		:param task_cls: if it is specified then result will be consists of this subclass only
  
  		:return: None or WTask or tuple of WTask
  		"""
  
  		if task_registry_id is not None:
  			task = None
  			for registered_task in self.__started:
  				if registered_task.__registry_tag__ == task_registry_id:
  					task = registered_task
  
  			if task_cls is not None and task is not None:
  				if isinstance(task, task_cls) is True:
  					return task
  				return None
  			return task
  
  		result = filter(lambda x: x is not None, self.__started)
  		if task_cls is not None:
  			result = filter(lambda x: isinstance(x, task_cls), result)
  		return tuple(result)