Feature Request: cross-location boolean search

Which is to say, a little more like Mail – for instance, in searching a mailbox, being able to search for “frogs” in messages from “steven”?

Yes, being able to specify where to search is on my to-do list. At present, you could search for “frogs steven”, which should find the messages you’re interested in, as well as other messages containing both those words. And you can also search for “tag:steven frogs”, which would find the messages tagged “steven” that contain the word “frogs”.

As of EagleFiler 1.4, you can do this using smart folders.