Rule for an IP version 4 style address
<boost/url/rfc/ipv4_address_rule.hpp>
constexpr /* implementation-defined */ ipv4_address_rule = {};
using value_type = ipv4_address;
Rules are used with the function grammar::parse.
system::result< ipv4_address > rv = grammar::parse( "192.168.0.1", ipv4_address_rule );
IPv4address = dec-octet "." dec-octet "." dec-octet "." dec-octet
dec-octet   = DIGIT                 ; 0-9
            / %x31-39 DIGIT         ; 10-99
            / "1" 2DIGIT            ; 100-199
            / "2" %x30-34 DIGIT     ; 200-249
            / "25" %x30-35          ; 250-255