1 files changed, 5 insertions, 2 deletions
diff --git a/lisp/rot13.el b/lisp/rot13.el
index ee4f51d7ff3..d0e4048ad61 100644
--- a/lisp/rot13.el
+++ b/lisp/rot13.el
@@ -1,4 +1,4 @@
-;;; rot13.el --- display a buffer in ROT13
+;;; rot13.el --- display a buffer in ROT13  -*- lexical-binding: t -*-
 
 ;; Copyright (C) 1988, 2001-2016 Free Software Foundation, Inc.
 
@@ -63,7 +63,10 @@
 
 ;;;###autoload
 (defun rot13 (object &optional start end)
-  "Return ROT13 encryption of OBJECT, a buffer or string."
+  "ROT13 encrypt OBJECT, a buffer or string.
+If OBJECT is a buffer, encrypt the region between START and END.
+If OBJECT is a string, encrypt it in its entirety, ignoring START
+and END, and return the encrypted string."
   (if (bufferp object)
       (with-current-buffer object
 	(rot13-region start end))