Clojurians Log v2

Can someone point me to documentation about how the [:find [?e ...] and related syntax works? Specifically I'm referring to the "bracket ?e ellipsis" bit. I don't quite understand the semantics there. If I want to pull out the entity id of an entity from a query that I expect to only return a single result, I end up with a result like [1] and I have to call first to get the id out. I want to avoid the call to first by learning how that ellipsis syntax works.