guides/custom-permissions.md

@@ -100,3 +100,24 @@ class Circle(Model):
     class Meta(Model.Meta):
         permission_classes = [CirclePermissions]
 ```
+
+### Custom FilterBackends
+
+In DjangoLDP 1.3.0, permissions are changing so that `user_permissions` are not resolved on the model-level during serialization, to improve extensibility and performance
+
+Users familiar with Django Rest Framework will be familiar with [FilterBackends](https://www.django-rest-framework.org/api-guide/filtering/#generic-filtering), which are used in a view's `filter_queryset` to remove objects which a user shouldn't see. In DjangoLDP, filter backends can be included on a permission class, and the result will be automatically applied to any views and models using the permission class
+
+By default, `LDPPermissions` subclasses include a filter backend which applies model-level permissions (`owner_perms`, `auth_perms`, `anon_perms`) object-level permissions and group-level permissions:
+```python
+filter_backends = [LDPPermissionsFilterBackend]
+```
+
+This functionality can be disabled by setting the `filter_backends` of your permissions class to an empty list
+```python
+filter_backends = []
+```
+
+It can be extended by writing a custom `FilterBackend`, and applying it to the list
+```python
+filter_backends = [MyCustomFilterBackend, LDPPermissionsFilterBackend]
+```
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