Emphasized that ForeignKey.on_delete doesn't create a SQL constraint.
@@ -1271,6 +1271,9 @@ relation works.
null=True,
)
+ ``on_delete`` doesn't create a SQL constraint in the database. Support for
+ database-level cascade options :ticket:`may be implemented later <21961>`.
+
The possible values for :attr:`~ForeignKey.on_delete` are found in
:mod:`django.db.models`:
