Explain vc-BACKEND-root in Commentary; nfc.

diff --git a/lisp/vc.el b/lisp/vc.el
index 3376113711a1f2af660cafb905c3cd3071f99719..1af8bfc80c0d657b971b044ee909434b2c899795 100644 (file)
--- a/lisp/vc.el
+++ b/lisp/vc.el
@@ -465,6 +465,12 @@
 ;;
 ;; MISCELLANEOUS
 ;;
+;; - root (dir)
+;;
+;;   Return DIR's "root" directory, that is, a parent directory of
+;;   DIR for which the same backend as used for DIR applies.  If no
+;;   such parent exists, this function should return DIR.
+;;
 ;; - make-version-backups-p (file)
 ;;
 ;;   Return non-nil if unmodified repository revisions of FILE should be