AdamR: "What we want is a delegation model that allows third parties to mint new, guaranteed unique identifiers for their payment methods"
Tab: "URNs are thus purely downside due to increased verbosity."
Tab: "[Use] plain identifiers from a registry if all you need is a way to uniquely identify things; plain origins if you just need it for a reasonable security/identity boundary that's shared across web and apps (and is obviously not meant to be resolved, since it's just pointing at a homepage); or URLs if and only if you're actually using what's at the end of the URL for something worthwhile"
Requirement: Some assurance of authenticity of payment app to support a proprietary payment method (e.g., based on origin)
Question: Do we want proprietary payment method owners to be able to delegate authority to other origins to implement apps that support the method?
Zach: I want to be able to prevent arbitrary payment apps for claiming support for proprietary payment methods. If we can't prevent this, we're going to have a hard time convincing existing players to enter into our ecosytem, which makes adoption by merchants more difficult.
Zach: We both want payment methods that are completely open, somewhat open, and not open at all to be able to play in the ecosystem.