The format of the alt parameter is strictly defined by [RFC 7838][] as an ASCII string containing a comma-delimited list of “alternative” protocols associated with a specific host and port.

    For example, the value 'h2="example.org:81"' indicates that the HTTP/2 protocol is available on the host 'example.org' on TCP/IP port 81. The host and port must be contained within the quote (") characters.

    Multiple alternatives may be specified, for instance: 'h2="example.org:81", h2=":82"'.

    The protocol identifier ('h2' in the examples) may be any valid [ALPN Protocol ID][].

    The syntax of these values is not validated by the Node.js implementation and are passed through as provided by the user or received from the peer.