Also a fair point.

The original reason for using Arrays (and something that still carries some weight with me), is that people expected that Arrays be presented in a particular order returned by the server. Indeed, the semantics of a to-many relationship need to be set-like (in order to avoid nasty concurrent modification issues), but people really wanted the ability to return an array and have it "work as expected". In general, the right way to handle position, imho, is to use a `position` attribute and sort on the client. After saying all of that, perhaps this is a good reason to use ID indices, so people don't get the wrong idea.

I'll sleep on it :)