Google Japan KK RFC 7556 [RFC7556] provides the essential conceptual guidance an API designer would need to support use of PvDs. This document aims to capture the requirements for an API that can be used by applications that would be considered "advanced", according to section 6.3 [1] of RFC 7556 [RFC7556]. The "basic" [2] and "intermediate" [3] API support levels can in principle be implemented by means of layers wrapping the advanced API.