Re: master e37eb7f: Add support for pixel wheel deltas on NS

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Sat, 27 Nov 2021 19:44:15 +0800
> 
> > 	if (CONSP (event->arg))
> > 	  return list5 (head, position, make_fixnum (double_click_count),
> > 			XCAR (event->arg), Fcons (XCAR (XCDR (event->arg)),
> > 						  XCAR (XCDR (XCDR (event->arg)))));
> >
> > ?  If so, this always produces a 5-element list, and CLICKS is always
> > included.  Right?
> 
> Yes, but event->arg might not always be a cons.  On X, it is only a cons
> in XInput 2 events that have precise scrolling information.  When
> handling legacy events, it is nil.

I did mean what happens when the precise scrolling information is
there.

> AFAIU (and this may not be a very accurate understanding), if event->arg
> is a cons, it means it might have line scroll information, and has pixel
> scroll information.
> 
> Otherwise, if it is a number, it has only line information.
> 
> Otherwise, if the wheel event is double or triple, `double_click_count'
> will be included.
> 
> And otherwise, only the event name and position will be included.

So I think the manual should describe these possibilities, i.e. that
every member past POSITION can be present or absent, and if it's
present, the next one could be present or absent, etc.