parsing DNS zone with regexp::grammars

gistfile1.pl

#! /usr/bin/perl
use Modern::Perl;
use YAML;
# Net::Grammars::Digzone;
# possible bugs: no empty line available

# http://en.wikipedia.org/wiki/List_of_DNS_record_types
my $parse_dig_zone = do {
    use Regexp::Grammars;
    qr{ 
    \A (?: <[record]>
        | <.comment=(?: [;][^\n]+\n )> 
        )+
    \z

    <rule:record>
        <simplerecord>
        | <srvrecord>
        | <soarecord>
        | <txtrecord>

    # http://en.wikipedia.org/wiki/SRV_record#Record_format 
    <rule:srvrecord>
        [_] <service=ident>
        [.][_] <proto=(tcp | udp )>
        [.] <name=hostname>
        <ttl=num> IN SRV
        <priority=num> 
        <weight=num> 
        <port=num> 
        <target=hostname> 
        \n
    <rule:txtrecord>
        <entry=hostname>
        <ttl=num> IN TXT
        \" <txt=(?:[^\n]+)> \" \s* \n

    <rule:soarecord>
        <entry=hostname>
        <ttl=num> IN SOA
        <contact=hostname>
        <serial=num> 
        <refresh=num> 
        <retry=num> 
        <expiry=num> 
        <rrttl=num> 
        \n

    <rule:simplerecord>
        <entry=hostname>
        <ttl=num> IN <simplerecordtype>
        <value=hostname>
        \n

    <rule:mxrecord>
        <entry=hostname>
        <ttl=num> IN <simplerecordtype>
        <value=hostname>
        <priority=num>
        \n

    <rule:simplerecordtype> ( NS | CNAME | A | AAAA )
    <rule:hostname> <.ident>(.<.ident>)*.?
    <token:num> \d+
    <token:ident> ( [-a-z0-9]+ | \* ) 

    }xsm
};