Issue #15261: Stop os.stat(fd) crashing on Windows when fd not open.
diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index 7821628..20a84b6 100644
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -70,11 +70,16 @@
 
 .. function:: exists(path)
 
-   Return ``True`` if *path* refers to an existing path.  Returns ``False`` for
-   broken symbolic links. On some platforms, this function may return ``False`` if
-   permission is not granted to execute :func:`os.stat` on the requested file, even
+   Return ``True`` if *path* refers to an existing path or an open
+   file descriptor.  Returns ``False`` for broken symbolic links.  On
+   some platforms, this function may return ``False`` if permission is
+   not granted to execute :func:`os.stat` on the requested file, even
    if the *path* physically exists.
 
+   .. versionchanged:: 3.3
+      *path* can now be an integer: ``True`` is returned if it is an
+       open file descriptor, ``False`` otherwise.
+
 
 .. function:: lexists(path)