Comment 2 for bug 1637203

Yeah. The "mini-language" (which we call 'specifiers') is under-documented (and not as robust as I would like, and doesn't cover all objects in MAAS) because it was developed rapidly in order to meet the requirements for the 'interfaces' constraint.

I do think we should make it more robust and more available to all applicable APIs. But this is more a wishlist for a future release than a bug fix, in my mind.