The Web Payments Working Group have published Recommendations of Payment Request API and Payment Method Identifiers.
Payment Request standardizes an API to allow merchants (i.e., web sites selling physical or digital goods) to utilize one or more payment methods with minimal integration. Browsers facilitate the payment flow between merchant and user. Payment Method Identifiers defines payment method identifiers and how they are validated, and, where applicable, minted and formally registered with the W3C.
Please see the disposition of comments following review by the W3C Membership.