diff-update-on-the-fly doc string clarification

* lisp/vc/diff-mode.el (diff-update-on-the-fly): Mention what the
nil value does (bug#43297).

diff --git a/lisp/vc/diff-mode.el b/lisp/vc/diff-mode.el
index f223ae48f3b7e4d9ec292905bb2fe61ccb7f4232..d586afb97b0ef75f1fdd807d101cb933ad4ae736 100644 (file)
--- a/lisp/vc/diff-mode.el
+++ b/lisp/vc/diff-mode.el
@@ -83,7 +83,10 @@ When editing a diff file, the line numbers in the hunk headers
 need to be kept consistent with the actual diff.  This can
 either be done on the fly (but this sometimes interacts poorly with the
 undo mechanism) or whenever the file is written (can be slow
-when editing big diffs)."
+when editing big diffs).
+
+If this variable is nil, the hunk header numbers are updated when
+the file is written instead."
   :type 'boolean)
 
 (defcustom diff-advance-after-apply-hunk t