2.6 The //*MSG Control Card
The "//*MSG" execution-time control card allows you to selectively halt/resume 'typing on the job output' or to discard messages which have been previously output during execution of the job. Note that the latter option has no effect when the output of the job is sent as interactive messages, as it is intended to control mail job output.
The syntax of the "//*MSG" control card is:
Valid options are: ON, OFF, FLUSH
FLUSH discards all messages previously sent to the job output and leaves the message-receipt status unchanged.
OFF turns message receipt off, as if "Reply-to=None" had been specified in the JOB card.
ON turns message receipt back on. This does NOT override a possible "Reply-to=None" in the JOB card, though.