#6324: membership test tries iteration via __iter__.
diff --git a/Doc/reference/datamodel.rst b/Doc/reference/datamodel.rst
index 6a7acf9..3f9b181 100644
--- a/Doc/reference/datamodel.rst
+++ b/Doc/reference/datamodel.rst
@@ -1888,12 +1888,16 @@
supply the following special method with a more efficient implementation, which
also does not require the object be a sequence.
-
.. method:: object.__contains__(self, item)
- Called to implement membership test operators. Should return true if *item* is
- in *self*, false otherwise. For mapping objects, this should consider the keys
- of the mapping rather than the values or the key-item pairs.
+ Called to implement membership test operators. Should return true if *item*
+ is in *self*, false otherwise. For mapping objects, this should consider the
+ keys of the mapping rather than the values or the key-item pairs.
+
+ For objects that don't define :meth:`__contains__`, the membership test first
+ tries iteration via :meth:`__iter__`, then the old sequence iteration
+ protocol via :meth:`__getitem__`, see :ref:`this section in the language
+ reference <membership-test-details>`.
.. _sequence-methods: