make-backup-file-name--default-function
make-backup-file-name--default-function is a compiled Lisp function in `files.el
'.
(make-backup-file-name--default-function FILE)
Default function for `make-backup-file-name'.
Normally this just returns FILE's name with `~' appended.
It searches for a match for FILE in `backup-directory-alist'.
If the directory for the backup doesn't exist, it is created.