diff -r 037253b7cd6d Doc/library/socket.rst
--- a/Doc/library/socket.rst    Fri Oct 02 13:14:03 2015 +0300
+++ b/Doc/library/socket.rst    Fri Oct 02 14:45:48 2015 +0300
@@ -384,7 +384,11 @@
    :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
    constants. The protocol number is usually zero and may be omitted or in the
    case where the address family is :const:`AF_CAN` the protocol should be one
-   of :const:`CAN_RAW` or :const:`CAN_BCM`.
+   of :const:`CAN_RAW` or :const:`CAN_BCM`. If fileno is specified, the other
+   arguments are ignored, causing the socket with the specified file descriptor
+   to return. Unlike :meth:`fromfd`, fileno will return the same socket and not
+   a duplicate. This may help close a detached socket using
+   :meth:`socket.close()`.
 
    The newly created socket is :ref:`non-inheritable <fd_inheritance>`.