bug#11011: Binding S-TAB

[Eli Zaretskii]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Thu, 20 Aug 2020 12:06:44 -0700
> Cc: 11011@debbugs.gnu.org
> 
> 0. emacs -Q
> 1. (global-set-key (kbd "S-TAB") (lambda () (message "FOO")))
> 2. S-TAB
> 
> And see the following error: "<backtab> is undefined"

You say "S-TAB", but that's not the key you pressed.  You pressed
<backtab>, a function key, whereas S-TAB is a shifted ASCII character.
Try "C-S-i" instead (which will also reveal a minor unrelated bug in
your recipe ;-).