Index: wp-includes/functions.php
===================================================================
--- wp-includes/functions.php	(revision 20292)
+++ wp-includes/functions.php	(working copy)
@@ -1504,7 +1504,8 @@
  * unique.
  *
  * The callback is passed three parameters, the first one is the directory, the
- * second is the filename, and the third is the extension.
+ * second is the filename, and the third is an optional supplied callback
+ * to generate a unique file name.
  *
  * @since 2.5.0
  *