is uniqueConstraint.js isolated across a single collection?

[steve-torchia]

We need per-collection (not per-partition) uniqueness for our problem domain. I just want to confirm that uniqueConstraint.js is indeed safe for that. For example if two creates come in at the same time with the same unique value, one will win and the other will return to the calling client with a "unique constraint violation" or something similar.

thank you!