subr.el (remove-yank-excluded-properties): Explain in a comment why `category'

 property is removed.

lisp/ChangeLog

+2010-02-20  Eli Zaretskii  <eliz@gnu.org>
+
+	* subr.el (remove-yank-excluded-properties): Explain in a comment
+	why `category' property is removed.
+
 2010-02-19  Chong Yidong  <cyd@stupidchicken.com>
 
 	* isearch.el (isearch-update-post-hook, isearch-update): Revert

lisp/subr.el

@@ -2442,7 +2442,11 @@ Otherwise, return nil."
   "Remove `yank-excluded-properties' between START and END positions.
 Replaces `category' properties with their defined properties."
   (let ((inhibit-read-only t))
-    ;; Replace any `category' property with the properties it stands for.
+    ;; Replace any `category' property with the properties it stands
+    ;; for.  This is to remove `mouse-face' properties that are placed
+    ;; on categories in *Help* buffers' buttons.  See
+    ;; http://lists.gnu.org/archive/html/emacs-devel/2002-04/msg00648.html
+    ;; for the details.
     (unless (memq yank-excluded-properties '(t nil))
       (save-excursion
 	(goto-char start)