Subject: bug#79323: 30.2; Control-X-prefix not remapable

From: Juri Linkov <[email-masked]>
Date: Thu, 28 Aug 2025 22:07:20 +0300

>  (defvar-keymap tab-line-mode-map
>    :doc "Keymap for keys of `tab-line-mode'."
> +  :parent ctl-x-map
> +  "<left>"    #'tab-line-switch-to-prev-tab
> +  "C-<left>"  #'tab-line-switch-to-prev-tab
> +  "M-<left>"  #'tab-line-move-tab-backward
> +  "<right>"   #'tab-line-switch-to-next-tab
> +  "C-<right>" #'tab-line-switch-to-next-tab
> +  "M-<right>" #'tab-line-move-tab-forward)

Actually, this doesn't work.  And this doesn't work too:

diff --git a/lisp/tab-line.el b/lisp/tab-line.el
index 7caae8bc2c1..b9eb3b967c7 100644
--- a/lisp/tab-line.el
+++ b/lisp/tab-line.el
@@ -1279,12 +1279,13 @@ tab-line-event-start
 
 (defvar-keymap tab-line-mode-map
   :doc "Keymap for keys of `tab-line-mode'."
-  "C-x <left>"    #'tab-line-switch-to-prev-tab
-  "C-x C-<left>"  #'tab-line-switch-to-prev-tab
-  "C-x M-<left>"  #'tab-line-move-tab-backward
-  "C-x <right>"   #'tab-line-switch-to-next-tab
-  "C-x C-<right>" #'tab-line-switch-to-next-tab
-  "C-x M-<right>" #'tab-line-move-tab-forward)
+  :prefix 'ctl-x-map
+  "<left>"    #'tab-line-switch-to-prev-tab
+  "C-<left>"  #'tab-line-switch-to-prev-tab
+  "M-<left>"  #'tab-line-move-tab-backward
+  "<right>"   #'tab-line-switch-to-next-tab
+  "C-<right>" #'tab-line-switch-to-next-tab
+  "M-<right>" #'tab-line-move-tab-forward)

Probably there is no way to do this with 'defvar-keymap'?
This leaves only one solution with

  (define-key ctl-x-map ...