define-key doesn't seem to work on certain keymap

Question

I'm trying to add some bindings to undo-tree-visualizer-mode-map. To do so I use:

(define-key undo-tree-visualizer-mode-map (kbd "S-l") 'undo-tree-visualizer-quit)

But it doesn't work, and if I do describe-keymap afterwards I see that the binding wasn't added.

There seems to be a few keymap where this behavior happens, such as ivy-occur-mode-map and Info-mode-map as well.

Any idea why is that? And how can I add bindings to those keymaps?

Answer 1

S-l

You need to use L rather than S-l.

This is a quirk of key sequences in Emacs -- for letters (a-z), the shift modifier syntax S- won't do what you want, unless C- is also used in the sequence.

You should therefore write upper-case letters explicitly in key sequences.

See also https://stackoverflow.com/q/38180797/324105

For clarity:

(kbd "L")
"L"

(kbd "S-l")
[33554540]

(kbd "C-l")
"^L"

(kbd "C-L")
"^L"

(kbd "C-S-l")
[33554444]

Arguably Emacs ought to translate [33554540] to "L", or otherwise recognise it as intended, but in practice (at least at present) that doesn't happen.