Is the following request allowed:
Where a new article is created and in the response body, the newly created article is returned along with an included array including all related authors to that new article?
From the spec:
An endpoint MAY also support an include request parameter to allow the client to customize which related resources should be returned.
Note: This section applies to any endpoint that responds with primary data, regardless of the request type. For instance, a server could support the inclusion of related resources along with a POST request to create a resource or relationship.