This is the default behaviour; the option is provided to
override any configuration settings.
+`git mergetool` creates `*.orig` backup files while resolving merges.
+These are safe to remove once a file has been merged and its
+`git mergetool` session has completed.
+Setting the `mergetool.keepBackup` configuration variable to `false`
+causes `git mergetool` to automatically remove the backup as files
+are successfully merged.
Written by Theodore Y Ts'o <firstname.lastname@example.org>