Smarter folders - full boolean search

Description

Smart folders are great, but now I want to create one with more complex selection criteria than currently supported.

The current design is nice and simple and works for many kinds of selections you might want to do, but now I need something better. Specifically, in my GTD system, I have entries tagged as na (next actions) and each fits into at least one context (the context field on an entry might be "computer phone home" to mean it can be done at the computer at home when I have access to the phone). It's easy enough to find all next actions and to create a smart folder of just those next actions that are in one context (or not in one context), but I need to create a smart folder like this:

GTD contains "na" and (context contains "school" or context contains "computer" or context contains "phone")

but there's no way to do that currently. So, I propose two possible solutions:

Nested Smart Folders

By allowing nested smart folders this will solve the problem because I can apply further criteria to the entries already selected for a smart folder. This is nice because it fits with how smart folders already work in Mori (select from the entries at the same level as them and down, but never up) and doesn't make the selection criteria panel any more complicated.

Nested Selection Criteria

I've seen a few programs do this before. To support more complex selection criteria, they allow for the creation of a parentheses entry in the list, i.e. it say something like "meets (any|all)" and then normal selection criteria can appear inside of it. This does make the selection criteria panel more complex, but it makes smart folders with selection criteria possible without deeply nesting smart folders.