Try to clarify the filter information on /context

api/client-server/event_context.yaml

@@ -63,10 +63,9 @@ paths:
           name: filter
           type: string
           description: |-
-            The ID of a filter created using the filter API or a filter JSON
+            A JSON ``RoomEventFilter`` to filter the returned events with. The
-            object encoded as a string. The server will detect whether it is
+            filter can be applied before or/and after the ``limit`` parameter -
-            an ID or a JSON object by whether the first character is a ``"{"``
+            whichever the homeserver prefers.
-            open brace.
 
             See `Filtering <#filtering>`_ for more information.
           x-example: "66696p746572"