[comp.windows.x] why is Xlib V11's error handler a function of type int?

oj@apollo.uucp (Ellis Oliver Jones) (12/20/87)

The XSetErrorHandler documentation in the Xlib manual, section
8.10.2, states that a user-specified error handler should be
a function of type int.
However, X.V11R1/lib/X/XNextEvent.c discards the function
return value from _XError, which in turn comes from the
error handler.  Likewise, all the other callers of _XError
discard the return value.  The default error handler returns 0.

So, my question is--was there some reason (such as the extension
mechanism) that error handlers were functions?  Is there a meaning
(albeit nothing but hooks to the future) assigned to non-zero return
values?  Thanks.
/oj/Apollo Computer, Inc./