Doc updates for buffer-stale-function now applying to file buffers too

* doc/emacs/arevert-xtra.texi (Supporting additional buffers):
* doc/lispref/backups.texi (Reverting):
Update for buffer-stale-function also applying to file-buffers.

* lisp/autorevert.el (auto-revert-buffers):
* lisp/files.el (buffer-stale--default-function)
(buffer-stale-function, revert-buffer--default): Doc tweaks.

* etc/NEWS: Related edits.

2 files changed, 5 insertions, 1 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index 456c2cbdc12..1fb664893f8 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -2,6 +2,8 @@
 
         * backups.texi (Making Backups, Reverting):
         Update for default values of some -function vars no longer being nil.
+        (Reverting): Update for buffer-stale-function
+        also applying to file-buffers.
 
 2014-03-25  Eli Zaretskii  <eliz@gnu.org>
 
diff --git a/doc/lispref/backups.texi b/doc/lispref/backups.texi
index 9fa97fc1300..63f8f227c84 100644
--- a/doc/lispref/backups.texi
+++ b/doc/lispref/backups.texi
@@ -764,7 +764,9 @@ may or may not run this hook.
 @c FIXME?  Move this section from arevert-xtra to here?
 @defvar buffer-stale-function
 The value of this variable specifies a function to call to check
-whether a non-file buffer needs reverting
+whether a buffer needs reverting.  The default value only handles
+buffers that are visiting files, by checking their modification time.
+Buffers that are not visiting files require a custom function
 @iftex
 (@pxref{Supporting additional buffers,,, emacs-xtra,  Specialized Emacs Features}).
 @end iftex