bpo-38531: document extend action's added version (GH-16865)
diff --git a/Doc/library/argparse.rst b/Doc/library/argparse.rst
index 00115d5..818acf4 100644
--- a/Doc/library/argparse.rst
+++ b/Doc/library/argparse.rst
@@ -838,6 +838,8 @@
>>> parser.parse_args(["--foo", "f1", "--foo", "f2", "f3", "f4"])
Namespace(foo=['f1', 'f2', 'f3', 'f4'])
+ .. versionadded:: 3.8
+
You may also specify an arbitrary action by passing an Action subclass or
other object that implements the same interface. The ``BooleanOptionalAction``
is available in ``argparse`` and adds support for boolean actions such as