# Constants
Nack_Park means to park the message and do not resend.
Nack_Retry means explicitly retry the message.
Nack_Skip means to skip this message, do not resend and do not put in poison queue.
Nack_Stop is meanT to stop the subscription.
Nack_Unknown means that the client does not know what action to take.
# Type aliases
Nack_Action represents a reason why message was nack-ed.