Issue #12760: Refer to the new 'x' open mode as "exclusive creation" mode.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index 82969eb..e1268cb 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -472,12 +472,12 @@
to which the resulting :class:`FileIO` object will give access.
The *mode* can be ``'r'``, ``'w'``, ``'x'`` or ``'a'`` for reading
- (default), writing, creating or appending. The file will be created if it
- doesn't exist when opened for writing or appending; it will be truncated
- when opened for writing. :exc:`FileExistsError` will be raised if it already
- exists when opened for creating. Opening a file for creating implies
- writing, so this mode behaves in a similar way to ``'w'``. Add a ``'+'`` to
- the mode to allow simultaneous reading and writing.
+ (default), writing, exclusive creation or appending. The file will be
+ created if it doesn't exist when opened for writing or appending; it will be
+ truncated when opened for writing. :exc:`FileExistsError` will be raised if
+ it already exists when opened for creating. Opening a file for creating
+ implies writing, so this mode behaves in a similar way to ``'w'``. Add a
+ ``'+'`` to the mode to allow simultaneous reading and writing.
The :meth:`read` (when called with a positive argument), :meth:`readinto`
and :meth:`write` methods on this class will only make one system call.
diff --git a/Doc/whatsnew/3.3.rst b/Doc/whatsnew/3.3.rst
index b2909f7..a60e585 100644
--- a/Doc/whatsnew/3.3.rst
+++ b/Doc/whatsnew/3.3.rst
@@ -427,8 +427,9 @@
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`)