#!perl

use 5.012; # strict, //
use warnings;
use Data::Dump;
use XML::Rules;

my $xml_doc = <<EOXML;
<?xml version="1.0" encoding="UTF-8" ?>
<!-- important instructions to manual editors -->
<root>
    <group name="blah">
        <!-- important instructions for group "blah" -->
        <tag/>
    </group>
    <group name="second">
        <!-- important instructions for group "second" -->
        <differentTag/>
    </group>
</root>
EOXML

my $callback = sub {
    my ($name, $parser, @args) = @_;
    print STDERR "event:", $name//'<undef>', "(";
    print STDERR join ', ', map {defined($_) ? qq("$_") : '<undef>'} @args;
    print STDERR ")\n";
};

my %handlers = ();
for my $h ( qw/Comment XMLDecl/ ) { #qw/Start End Char Proc Comment CdataStart CdataEnd Default Unparsed Notation ExternEnt ExternEntFin Entity Element Attlist Doctype DoctypeFin XMLDecl/) {
    $handlers{$h} = sub { $callback->($h => @_) }
}

my $parser = XML::Rules->new(
    stripspaces => 3|4,
    rules => [
        _default => 'raw',
    ],
    handlers => \%handlers,
);

#dd
my $data = $parser->parse($xml_doc);

print
my $out = $parser->ToXML($data, 0, "  ", "") . "\n";

__DATA__

event:XMLDecl("1.0", "UTF-8", <undef>)
event:Comment(" important instructions to manual editors ")
event:Comment(" important instructions for group "blah" ")
event:Comment(" important instructions for group "second" ")
<root>
  <group name="blah">
    <tag/>
  </group>
  <group name="second">
    <differentTag/>
  </group>
</root>