Register contents when Exit 21 passes control back to JES2

Upon return from this exit, the register contents must be:

A return code of:

0: Tells JES2 that if any additional exit routines are associated with this exit, call the next consecutive exit routine. If no additional exit routines are associated with this exit continue normal SMF queue processing.
4: Tells JES2 to ignore any other exit routines associated with this exit and to continue normal SMF queue processing.
8: Tells JES2 to terminate normal SMF queue processing.