The patch in #91, by using a patch path including a zero-based index into the returned results from a GET, seems to formalize the notion that collections are ordered.

Are collections required to be ordered? Even if so, not referencing the record by ID seems to be begging for race conditions. What if a new document is inserted earlier in the collection between a GET request and it's corresponding PATCH?

At the bottom of "Updating a Document (PATCH)" > "To-Many Relationships" it is made explicit that "to-many relationships have set-like behavior in JSON API to limit the damage that can be caused by concurrent modifications." It seems collections should behave the same way, but instead collections are repeatedly referred to as "arrays" or "lists" (implying order) in the "singular resources" and "resource collections" sections.

Mind clarifying?