--- a/Doc/whatsnew/3.3.rst	Wed Jan 11 21:00:48 2012 -0500
+++ b/Doc/whatsnew/3.3.rst	Thu Jan 12 07:35:13 2012 +0200
@@ -411,8 +411,9 @@
 io
 --
 
-The :func:`~io.open` function has a new ``'x'`` mode that can be used to create
-a new file, and raise a :exc:`FileExistsError` if the file already exists.
+The :func:`~io.open` function has a new ``'x'`` mode that can be used to
+exclusively create a new file, and raise a :exc:`FileExistsError` if the file
+already exists. It is based on the C11 'x' mode to fopen().
 
 (Contributed by David Townshend in :issue:`12760`)