What's A Message

In general, a message is composed by the first token and message text: <first-token> <message-text>.

The message ID distinguishes a message from all others and typically appears as the first token. There are some exceptions that the actual message is wrapped by the outer message and hence the unique message ID appears within the message text. For a general description of messages, see Format of the message body in z/OS MVS System Messages Vol 1 (ABA-AOM).

SA requires a unique token to trap a particular message and that token is typically the message ID. Regardless of whether the message is wrapped or not, what matters to the users is the unique message ID that they would add in the policy.