Re: [webpayments] How should the message schemas for the payment request and response be defined? (#27)

@ianbjacobs,

> I agree. But "custom" says "We care enough to tell processors to leave this
data alone and not deal with it in some other way that might be processor-dependent."

I expect there to be more than one place where data can be extended. So we'd end up sprinkling "custom" bits just about everywhere. Either that, or people may end up having to duplicate bits of the payment message in the `custom` section, leading to bloat and potentially errors or confusion.

A compromise might be to say -- if you're extending via JSON-LD, then a `@context` must be present, which is also a trigger that means you can then extend however you want (with the obvious caveat that you can't stomp on well-defined properties). If no `@context` is present, you can throw errors for unrecognized properties.

---
Reply to this email directly or view it on GitHub:
https://github.com/w3c/webpayments/issues/27#issuecomment-178931759