emacs-29 327986936c3: Add index entry for fallback modes

[Robert Pluim]

branch: emacs-29
commit 327986936c3476bcfe930314e5d825c2ada55f49
Author: Robert Pluim <rpluim@gmail.com>
Commit: Robert Pluim <rpluim@gmail.com>

    Add index entry for fallback modes
    
    * doc/emacs/custom.texi (Specifying File Variables): Add index for
    'fallback modes'.
---
 doc/emacs/custom.texi | 1 +
 1 file changed, 1 insertion(+)

diff --git a/doc/emacs/custom.texi b/doc/emacs/custom.texi
index ee818a74b57..87290734cc9 100644
--- a/doc/emacs/custom.texi
+++ b/doc/emacs/custom.texi
@@ -1245,6 +1245,7 @@ Manual}.
 These four keywords are not really variables; setting them in any
 other context has no special meaning.
 
+@cindex fallback modes
   If you're editing a file across Emacs versions, and a new mode has
 been introduced to handle a file in a newer Emacs version, you can use
 several @code{mode} entries to use the new mode (called