When I had mentioned STCBUSER, I was a little surprised that no one asked "what about TCBUSER"?
No "protocol" was ever defined for TCBUSER in terms of "who is allowed to use it" so we have always felt it too dangerous to use ourselves (in case there are two conflicting potential users). The field exists; as the attacher or attachee you could probably get away with using it. But is "probably" enough? We tried to address that shortcoming within (much newer) field STCBUSER with the comment: Owner: target module of the ATTACH. Must be set only by that module or a module in its component Peter Relson z/OS Core Technology Design
