CD.EWS.04 message_type

Indicates the type of CAP message being sent.

Reference: CAP v1.2 Section 6.1.2

Code	Description
Alert	Initial or primary alert message.
Update	Updates or corrects an earlier alert.
Cancel	Cancels a previous alert.
Ack	Acknowledges receipt of a previous alert.
Error	Indicates an error in a previously sent alert.