Further down in the topic--way beyond the parameter defintions--is found this:[v1.1.20+]: Specify 0 to unregister a previously registered function. If Function is a string, the "legacy" monitor is removed. Otherwise, only the given function object is unregistered.
The fact that the Maxthreads parameter may be a NULL value to unregister a monitor should also be mentioned at Maxthreads.This unregisters the current legacy monitor for MsgNumber (if any) and returns its name (blank if none):
Name := OnMessage(MsgNumber, "")
Question: Is there any difference between Maxthread values of "" and 0? If not, I have to question why a NULL parameter (as opposed to no parameter ) is allowed. This is not very consistent with most (all?) other commands (and functions?). I suspect this is a backward compatability issue.