Allow limited attributes in relationship data?

[cmars]

While we do not want to allow compound documents as defined in JSON API, there is probably a case to be made for a small number of attributes that are useful/necessary for making "sense" of a relationship.

Allowing attributes here could be reasonable, if we can define the limits of when and how they should be applied.

Pitfalls seem to be:

• Dumping the entire contents of related entities out of laziness (so where to draw the line?)
• One-to-many (pagination of relationships is a definite no-go -- use GraphQL for that)

"Just use GraphQL for that" could be an answer to this question -- simply don't allow it -- but for a small number of fields, you're perhaps being pricinpled for its own sake and unhelpful...