I'm curious about this as well. I've always written frameworks to be used with a 'Policy Layer -> Mechanism Layer -> Utility Layer' general architecture. Each l

I'm curious about this as well. I've always written frameworks to be used with a 'Policy Layer -> Mechanism Layer -> Utility Layer' general architecture. Each layer captures and does its best to handle errors in a way you would expect that layer to. The only time errors move up towards the policy layer is explicitly because the next layer up will handle it.