Add weakref support to the thread.lock type.
diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
index 5dcb030..a1a3314 100644
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -65,6 +65,9 @@
.. versionchanged:: 2.4
Added support for files, sockets, arrays, and patterns.
+.. versionchanged:: 2.7
+ Added support for thread.lock and threading.Lock.
+
Several built-in types such as :class:`list` and :class:`dict` do not directly
support weak references but can add support through subclassing::