gh-132139: Document that you can no longer set attributes on unions (#132146)

diff --git a/Doc/whatsnew/3.14.rst b/Doc/whatsnew/3.14.rst
index 13448d1fc07654cfabac822a5a5b77166b128f43..b20d75c11807133c5438872934928c0f2f9ad77b 100644 (file)
--- a/Doc/whatsnew/3.14.rst
+++ b/Doc/whatsnew/3.14.rst
@@ -1130,6 +1130,8 @@ typing
     For example, ``isinstance(int | str, typing.Union)`` will return ``True``; previously
     this raised :exc:`TypeError`.
   - The ``__args__`` attribute of :class:`typing.Union` objects is no longer writable.
+  - It is no longer possible to set arbitrary dunder attributes on :class:`typing.Union`
+    objects.
 
   (Contributed by Jelle Zijlstra in :gh:`105499`.)