🚀 go-pugleaf

    The program, as listed in the book, uses -1L (XtAllEvents) for an event mask
    going into XSendEvent, and I believe that I read somewhere that R4 doesn't
    like this,

That is correct.  The mask must only indicate legal event bits, and -1
includes illegal bits.  The fact that Intrinsic.h has XtAllEvents defined
as -1 is probably a big mistake.

    so what else should I use???

I haven't actually tried it, and I've only spent a few seconds looking
at the example in the (non-Motif) book, but try just plain zero.  This
will cause the event to go to the owner of the remote_talker_window,
rather than following some arbitrary event mask.