Document batch-byte-compile directory behavior

* lisp/emacs-lisp/bytecomp.el (batch-byte-compile): Document the
behaviour with directories (bug#20867).

1 files changed, 8 insertions, 1 deletions

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 6dcd4c6846a..40b4e2f4671 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -5091,8 +5091,15 @@ it won't work in an interactive Emacs."
   "Run `byte-compile-file' on the files remaining on the command line.
 Use this from the command line, with `-batch';
 it won't work in an interactive Emacs.
-Each file is processed even if an error occurred previously.
+
+Each file is processed even if an error occurred previously.  If
+a file name denotes a directory, all Emacs Lisp source files in
+that directory (that have previously been compiled) will be
+recompiled if newer than the compiled files.  In this case,
+NOFORCE is ignored.
+
 For example, invoke \"emacs -batch -f batch-byte-compile $emacs/ ~/*.el\".
+
 If NOFORCE is non-nil, don't recompile a file that seems to be
 already up-to-date."
   ;; command-line-args-left is what is left of the command line, from