Document the Metadata API

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+<a class="github" href="metadata.py"></a>
+
+# Metadata
+
+> [The `OPTIONS`] method allows a client to determine the options and/or requirements associated with a resource, or the capabilities of a server, without implying a resource action or initiating a resource retrieval.
+>
+> &mdash; [RFC7231, Section 4.3.7.][cite]
+
+REST framework includes a configurable mechanism for determining how your API should respond to `OPTIONS` requests. This allows you to return API schema or other resource information.
+
+There are not currently any widely adopted conventions for exactly what style of response should be returned for HTTP `OPTIONS` requests, so we provide an ad-hoc style that returns some useful information.
+
+Here's an example response that demonstrates the information that is returned by default.
+
+    HTTP 200 OK
+    Allow: GET, POST, HEAD, OPTIONS
+    Content-Type: application/json
+
+    {
+        "name": "To Do List",
+        "description": "List existing 'To Do' items, or create a new item.",
+        "renders": [
+            "application/json",
+            "text/html"
+        ],
+        "parses": [
+            "application/json",
+            "application/x-www-form-urlencoded",
+            "multipart/form-data"
+        ],
+        "actions": {
+            "POST": {
+                "note": {
+                    "type": "string",
+                    "required": false,
+                    "read_only": false,
+                    "label": "title",
+                    "max_length": 100
+                }
+            }
+        }
+    }
+
+## Setting the metadata scheme
+
+You can set the metadata class globally using the `'DEFAULT_METADATA_CLASS'` settings key:
+
+    REST_FRAMEWORK = {
+        'DEFAULT_METADATA_CLASS': 'rest_framework.metadata.SimpleMetadata'
+    }
+
+Or you can set the metadata class individually for a view:
+
+    class APIRoot(APIView):
+        metadata_class = APIRootMetadata
+        
+        def get(self, request, format=None):
+            return Response({
+                ...
+            })
+
+The REST framework package only includes a single metadata class implementation, named `SimpleMetadata`. If you want to use an alternative style you'll need to implement a custom metadata class.
+
+## Creating schema endpoints
+
+If you have specific requirements for creating schema endpoints that are accessed with regular `GET` requests, you might consider re-using the metadata API for doing so.
+
+For example, the following additional route could be used on a viewset to provide a linkable schema endpoint.
+
+    @list_route(methods=['GET'])
+    def schema(self, request):
+        meta = self.metadata_class()
+        data = meta.determine_metadata(request, self)
+        return Response(data)
+
+There are a couple of reasons that you might choose to take this approach, including that `OPTIONS` responses [are not cacheable][no-options].
+
+---
+
+# Custom metadata classes
+
+If you want to provide a custom metadata class you should override `BaseMetadata` and implement the `determine_metadata(self, request, view)` method.
+
+Useful things that you might want to do could include returning schema information, using a format such as [JSON schema][json-schema], or returning debug information to admin users.
+
+## Example
+
+The following class could be used to limit the information that is returned to `OPTIONS` requests.
+
+    class MinimalMetadata(BaseMetadata):
+        """
+        Don't include field and other information for `OPTIONS` requests.
+        Just return the name and description.
+        """
+        def determine_metadata(self, request, view):
+            return {
+                'name': view.get_view_name(),
+                'description': view.get_view_description()
+            }
+
+[cite]: http://tools.ietf.org/html/rfc7231#section-4.3.7
+[no-options]: https://www.mnot.net/blog/2012/10/29/NO_OPTIONS
+[json-schema]: http://json-schema.org/