`M-x customize' feature wanted: compare default and customized values

[Matt Swift <swift@alum.mit.edu>]

This bug report will be sent to the Free Software Foundation,
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Please write in English, because the Emacs maintainers do not have
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In GNU Emacs 20.7.2 (i386-debian-linux-gnu, X toolkit)
 of Thu Apr  4 2002 on cyberhq modified by Debian
configured using `configure  i386-debian-linux-gnu --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib --localstatedir=/var/lib --infodir=/usr/share/info --mandir=/usr/share/man --with-pop=yes --with-x=yes --with-x-toolkit=yes'

Please describe exactly what actions triggered the bug
and the precise symptoms of the bug:

I'm making the transition to Emacs 21.2, and I notice it is missing a feature I
have sorely wanted in 20.7.  When using the customization interface, I very
much want to be able to compare the value of a previously-customized variable
to the default value.  The best way I can figure to do this now is to write
down or memorize the current value, then select "reset to standard value" and
compare what I then see with what I wrote down or memorized.  If I decide I did
want to use my original value, I have to type it in again (or cut-and-paste it
into the custom-file from a saved backup -- clunky and inconvenient no matter
what way you cut it).

Best of all would be the ability to display the two values side by side and to
diff them visually somehow, at least at the level of are they `equal' or not
(sometimes packages change their default to my customized value, which is now superfluous).

But satisfactory would be the ability to `M-x undo' the "reset to standard
settings option", an option to display the default value without erasing my
current one, an option to "revert to standard for this session", and so on --
any of these would be a huge boon.


Recent input:
2 C-x o C-l down-mouse-1 mouse-movement mouse-1 C-x 
k C-x k C-x 1 C-x C-f M-backspace C-a C-k $ e l m l 
/ s w i f t - c u s t tab . tab return C-s b i b t 
e x - m o d e - h o o k C-a C-n C-p M-f M-f M-f C-h 
v return switch-frame C-x C-s C-h v m a j o r - m o 
d tab return switch-frame M-x r e p o r t - e m a c 
s - b u g tab return

Recent messages:
Loading pp...
Loading pp...done
Loading /usr/lib/emacs/20.7/i386-debian-linux-gnu/fns-20.7.2.el (source)...
Loading /usr/lib/emacs/20.7/i386-debian-linux-gnu/fns-20.7.2.el (source)...done
Type C-x 1 to remove help window.  M-C-v to scroll the help.
Saving file /home/swift/information/todo-comp.out...
Wrote /home/swift/information/todo-comp.out
Type C-x 1 to remove help window.  M-C-v to scroll the help.
Loading emacsbug...
Loading emacsbug...done