| Valid value | Description |
|---|
| Ack | Acknowledges receipt and acceptance of the message(s)) identified in references |
| Alarm | Alarm message(s) |
| Alert | Initial information requiring attention by targeted recipients |
| Alert | Alert message(s) |
| Cancel | Cancels the earlier message(s) identified in references |
| Error | Indicates rejection of the message(s) identified in references; explanation SHOULD appear in note |
| Other | Other kind of message notification |
| Status | Status message(s) |
| Update | Updates and supersedes the earlier message(s) identified in references |
