If a file’s name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, …, foo.~259~, and so on.
This variable controls whether to make a single non-numbered backup file or multiple numbered backups.
nilMake numbered backups if the visited file already has numbered backups; otherwise, do not. This is the default.
neverDo not make numbered backups.
Make numbered backups.
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.
The value of this variable is the number of newest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function find-backup-file-name
(see Naming Backup Files) is responsible for determining which backup
versions to delete, but does not delete them itself.
If this variable is t, then saving a file deletes excess
backup versions silently. If it is nil, that means
to ask for confirmation before deleting excess backups.
Otherwise, they are not deleted at all.
This variable specifies how many of the newest backup versions to keep
in the Dired command . (dired-clean-directory). That’s the
same thing kept-new-versions specifies when you make a new backup
file. The default is 2.