key bindings for mouse wheel

["Drew Adams" <drew.adams@oracle.com>]

I've been using bindings such as this:

(define-key map [wheel-down]   'aaa)
(define-key map [wheel-down]   'bbb)
(define-key map [C-wheel-down] 'ccc)
(define-key map [C-wheel-down] 'ddd)

Reading some mail on (I think) help-gnu-emacs got me a bit confused however. It
gave me the impression that such bindings were only for MS Windows and that on
GNU/Linux `mouse-4' and `mouse-5' must be used instead of `wheel-down' and
`wheel-up'. (That sounds odd; I'd expect `mouse-4' and `mouse-5' to be a fourth
and fifth mouse button, as they are on Windows.)

I looked in the Elisp manual, but I didn't find anything specifically
recommending how one should bind mouse wheel events. I was assuming that
`wheel-down' was platform independent, but now I have a doubt.

The Elisp doc (node Misce Events) speaks about events such as (wheel-up
POSITION), but it doesn't speak about just what to use when binding such keys.
Further, it says that events such as (wheel-up POSITION) are not generated on
some systems and that on those systems "`mouse-4' and `mouse-5' are used
instead". (Why is that?)

It does say this, however: "For portable code, use the variables
`mouse-wheel-up-event' and `mouse-wheel-down-event'", and then it goes on to say
where those variables are defined (why?).

So after a bit of fiddling I switched to this:

(define-key map (vector mouse-wheel-down-event) 'aaa)
(define-key map (vector mouse-wheel-up-event)   'bbb)
(define-key map
  (vector (list 'control mouse-wheel-down-event)) 'ccc)
(define-key map
  (vector (list 'control mouse-wheel-up-event)) 'ddd)

I haven't tested on GNU/Linux, but I'm assuming this is what to use for portable
code. Am I missing something? Is there a shorter or better way to say this and
still be portable?

Does anyone else think:

1. There should be a shorter way to do this?

2. Or, if not, this should at least be documented clearly as the way to bind
mouse wheel events?

[I would even expect the Emacs manual to tell you how to bind mouse-wheel key
sequences... But AFAICT the Emacs manual isn't too helpful for even the basics
about key binding. I'm sending a separate mail about that.]