use XML::Rules;

my $parser = XML::Rules->new(
	rules => [
		_default => 'content',
		book => sub {
			my $title = delete $_[1]->{title};
			delete $_[1]->{'_content'};
			$title => $_[1],
		},
		bookstore => 'pass no content',
	]
);

my $data = $parser->parse(\*DATA);

use Data::Dumper;
print Dumper( $data);

__DATA__
<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
...

##</code><code>##

use XML::Rules;

my $parser = XML::Rules->new(
	rules => [
		_default => 'content',
		book => sub {
			return unless $_[1]->{category} eq $_[4]->{parameters};
			my $title = delete $_[1]->{title};
			delete $_[1]->{'_content'};
			$title => $_[1],
		},
		bookstore => 'pass no content',
	]
);

my $category = $ARGV[0] or die "Usage: BookStore2.pl category\n";

my $data = $parser->parse(\*DATA, $category);

use Data::Dumper;
print Dumper( $data);

__DATA__
<?xml version="1.0" encoding="ISO-8859-1"?>
<bookstore>
...

##</code><code>##

...
		book => sub {
			my ($tag, $attr, $context, $parents, $parser) = @_;
			return unless $attr->{category} eq $parser->{parameters};
			my $title = delete $attr->{title};
			delete $attr->{'_content'};
			$title => $attr,
		},
...