Name,Description,Reference
error,"The error parameter's value is a Token that is a proxy error
          type.  When present, it indicates that the intermediary encountered
          an issue when obtaining this response.",[RFC9209]
next-hop,"The next-hop parameter's value is a String or Token that
          identifies the intermediary or origin server selected (and used, if
          contacted) to obtain this response.  It might be a hostname, IP
          address, or alias.",[RFC9209]
next-protocol,"The next-protocol parameter's value indicates the Application-Layer
          Protocol Negotiation (ALPN) protocol identifier [RFC7301] of the protocol used by the intermediary to connect to the next hop when obtaining this response.",[RFC9209]
received-status,"The received-status parameter's value indicates the HTTP status code
          that the intermediary received from the next-hop server when
          obtaining this response.",[RFC9209]
details,"The details parameter's value is a String containing additional
          information not captured anywhere else.  This can include
          implementation-specific or deployment-specific information.",[RFC9209]
next-hop-aliases,"A string containing one or more DNS aliases or
          canonical names used to establish a proxied connection to the next
          hop.",[RFC9532]