files, or Mercurial repositories with a very large number of files.
For those backends which support it, setting @code{vc-async-checkin}
-to non-nil switches to doing checkin operations asynchronously. This is
-particularly useful as a directory local variable in repositories where
-checkin operations are slow
-(@pxref{Directory Local Variables,,,elisp,GNU Emacs Lisp Reference Manual}).
+to non-@code{nil} switches to doing checkin operations asynchronously.
+This is particularly useful as a directory local variable in
+repositories where checkin operations are slow (@pxref{Directory Local
+Variables,,,elisp,GNU Emacs Lisp Reference Manual}).
While an asynchronous checkin operation is in progress, if you use
@kbd{C-x C-s} to save a buffer visiting any file within the current VC