Panel redisplay occurs in either of these situations:
Redisplay occurs automatically after the )PROC section has been processed if the .MSG control variable is nonblank and the user has not requested END or RETURN. The .MSG control variable is set automatically if a translation or verification error occurs. It can also be set explicitly by use of an assignment statement in the )PROC section.
Redisplay occurs if a dialog function invokes the DISPLAY or TBDISPL service with no panel name specified (a blank).
See z/OS ISPF Services Guide under the description of TBDISPL for a explanation of how redisplay processing for the TBDISPL service differs from that for the DISPLAY service described here.