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

@halindrome,

I think there is a universal expectation to use JSON for messages. There is not, however, consensus to use JSON-LD. To foster adoption, I prefer a path that imposes the fewest constraints on the ecosystem. Therefore, I think we should define conformance to JSON, and allow that JSON to be JSON-LD where parties want to exchange JSON-LD.

The reason I mention an attribute like "custom" is to distinguish two cases:

 * Custom data that should be left alone in processing
 * Errors 

I do not feel strongly about this,  but it seems to me safer to distinguish those two cases
where we can. I would like to hear whether something like "custom" is a common pattern
in API design. I skimmed the API cookbook [1] but didn't see it there. (I didn't read the
document closely, so it might be in there somewhere.)

You wrote:

 "Just be descriptive about the things we care about, and permit the rest. "

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."

Ian




[1] https://www.w3.org/TR/api-design/


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