[h-e-w] mouse wheel support in Emacs 21.3.50

[Drew Adams]

GNU Emacs 21.3.50.1 (i386-mingw-nt5.1.2600) of 2004-07-26 on BERATUNG4,
Windows XP SP1.

1. Bug?: Searching Elisp Info for "wheel" shows nothing that is current. It
shows the same stuff as for Emacs 20 ("mouse-wheel"...). Yet, looking at
real mouse wheel events, I see stuff like wheel-up that is not in Info, and
I don't see "mouse-wheel" in real events.

2. What is the latest mouse wheel support? In this version of Emacs
(21.3.50.1), I see mwheel code with no version number, copyright ... 2002.
Is that the latest? Is there any doc for this, besides the source code
comments?

3. I'd like to know how to interpret the components of the various mouse
events. In Emacs 20 this was simple; there was just the POSITION and the
DELTA. Now I see lots of components (with no Elisp Info) - what does each
mean? In particular, if I call read-event and get mouse wheel events, where
can I get the DELTA info that used to be there?

Actually, I can pretty much see what's going on in mwheel-scroll, in terms
of getting the DELTA info (amount), but before I base new code on what
happens in (this 2002) mwheel-scroll code, I wonder if this is a good model;
that is, if this deals with the latest event structure and is the
recommended (i.e. current) way to go about things.

4. Also, how to interpret the various mouse wheel events that I see via
apropos, such as double-wheel-up? Double-clicking I understand, but what is
double-wheeling? And the whole treatment of the wheel as buttons 4 & 5 is
not clear to me. (I imagine that is behind this business of
double-wheeling.) And what if (as I do) I have 5 mouse buttons and a wheel?
I can see that mouse-4 and mouse-5 are correctly bound to real buttons, so
what is their relation to wheeling?

5. Finally, although I have little real hope for this, are there any
guidelines for trying to make code that deals with making the mouse wheel
work in both Emacs 20 and 21? Don't laugh; there are lots of people who use
GNU Emacs 20 - maybe as many as use XEmacs - and who will continue to do so
for one reason or another. It sometimes seems to me that the mapping
(upgrade path, compatibility matrix) between GNU Emacs versions is less well
documented than the mapping between current XEmacs and GNU Emacs. Maybe
that's the way it should be; maybe not. No holy war here, please.

Thanks,

  Drew