so the spec has implementation specific behavior that's not fully specified by just the spec?

i rather see they implement jsonpath - https://tools.ietf.org/id/draft-goessner-dispatch-jsonpath-0... instead of inventing their own xpath-like expression language tbh.

Edit: i suppose i shouldn't be surprised there's multiple standards to varying degrees of acceptance: https://datatracker.ietf.org/doc/html/rfc6901 so may be it is fine to use this expression language...