** Add a defcustom that supplies a function to name numeric backup files,
like make-backup-file-name-function for non-numeric backup files.
+** `dired-mode' should specify the semantics of `buffer-modified-p' for
+dired buffers and DTRT WRT `auto-revert-mode'.
+
* Important features:
** Having tabs above a window to switch buffers in it.