Event processing with Timeout 0

[lowry%aitg.DEC@decwrl.dec.com (David Lowry, VAX LISP 291-8070)]

I'm confused about what the correct behavior is when :timeout is 0 in
calls to EVENT-CASE, PROCESS-EVENT and EVENT-COND. 
My guess is it does the following:
 
  Check all the events in the event queue, and unless one of the clauses
or handlers returns non-nil, returns nil.  If discard-p is true, the
events that returned NIL are discarded.  Thus if timeout is 0 and 
discard-p is true and no events return non-NIL, the queue will be empty
afterwards.
 
I'm guessing this from the behavior of EVENT-LISTEN, and there does not
appear to be a way to clear unwanted events out of the queue and then 
return immediately.  So do I win the stuffed animal or go to the end of
the line?
 
D. Lowry
DEC