The PaymentAddress interface has a careOf field which is non-standard (no well-known address standards support it, see below). The careOf field is unnecessary, the recipient and organization fields sufficiently support all necessary use cases. Adding careOf poses significant issues in terms of interoperability with existing postal address schemas and APIs. (From spec discussion: https://github.com/w3c/browser-payment-api/issues/244)
Docs: https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/WhUAKyc0O80