<p>

In particular, the {{PaymentMethodData}}'s {{PaymentMethodData/data}}

and {{PaymentResponse}}'s {{PaymentResponse/details}} members allow

for the arbitrary exchange of data. In light of the wide range of

data models used by existing payment methods, prescribing data

specifics in this API would limit its usefulness. The

{{PaymentResponse/details}} member carries data from the payment

handler, whether Web-based (as defined by the [[[payment-handler]]])

or proprietary. The [=user agent=] MUST NOT support payment handlers

unless they include adequate user consent mechanisms (such as

awareness of parties to the transaction and mechanisms for

demonstrating the intention to share data).

</p>