REP-819 Keystone V3 Filter

The mess that is Keystone v3! Comment on _everything_ so we can get this fixed up. =)
I say keep the shorter names. I wouldn't specify it as lazy, becuase it's a single access anyway.

Lazy is usually indicative that you don't want to perform some expensive computation unless you need to. Getting a URI isn't expensive. We just want a shorter reference to that URI, because it's hit commonly. 

Personally, I'd take off the lazy keyword, and just have a val.