[#ACDEA9F7F68B0112FD4BD827D3693E33E8F6D6AF]
Return the IPv6 Zone ID
templateStringToken::result_type zone_id(StringToken&& token) const;
If the host type is host_type::ipv6 , this function returns the Zone ID as a string. Otherwise an empty string is returned. Any percent-escapes in the string are decoded first.
assert( url_view( "http://[fe80::1%25eth0]/" ).zone_id() == "eth0" );
Linear in `this->encoded_zone_id().size()`.
Calls to allocate may throw.
host = IP-literal / IPv4address / reg-name
IP-literal = "[" ( IPv6address / IPv6addrz / IPvFuture ) "]"
ZoneID = 1*( unreserved / pct-encoded )
IPv6addrz = IPv6address "%25" ZoneID