Really! I did not know this. We are quite incorrect in that regard then.

The spec was a little ambiguous, working to clear that up :) 

Looking into this.

Marcos: I believe the specs say that the browser is supposed to pass the response from  the payment handler to the merchant website unaltered and only parse the JSON string into a JavaScript object. Converting a part of that response into a PaymentAddress seems to overstep the responsibilities of the browser. What do you think?

As a spec solution, perhaps we could change the type of 'billingAddress' to 'object', but note that it's in PaymentAddress format.

> I believe the specs say that the browser is supposed to pass the response from the payment handler to the merchant website unaltered and only parse the JSON string into a JavaScript object. Converting a part of that response into a PaymentAddress seems to overstep the responsibilities of the browser. What do you think?

I'm not sure what you mean by overstepping here. Could you elaborate a bit? 

> As a spec solution, perhaps we could change the type of 'billingAddress' to 'object', but note that it's in PaymentAddress format.

See my OP about .toJSON(). It might also cause issues if `PaymentAddress` gains more methods/functionality in the future. 

 

> I'm not sure what you mean by overstepping here. Could you elaborate a bit?

Are browsers supposed to alter the payment app responses or validate them beyond JSON serializability? I do no think so. What's your opinion?

> Are browsers supposed to alter the payment app responses or validate them beyond JSON serializability? I do no think so. What's your opinion?

For basic card, at least, it's exactly the same behavior/validation/formatting that happens in: 
https://w3c.github.io/payment-request/#shipping-address-changed-algorithm

I'm going to move the address construction steps into its own algorithm, and I'll get Basic Card to hook into that. 
 
Now... for Payment Handler... that's a bit more complicated, so let's chat about that this week. 

Ok, so here is the split:
https://github.com/w3c/payment-request/pull/644

And here is the fix:
https://github.com/w3c/payment-method-basic-card/pull/45

`BasicCardResponse.billingAddress` was not specified at all! 😱 
Who is editing these things!? 🙃