use strict;
use warnings;
use XML::TreeBuilder;

my $doc = XML::TreeBuilder->new();
$doc->parse_file("minimal.xml");

my @vol = $doc->look_down(_tag => 'Volume', VolumeCategory => 'L');
# also tried various quoting scheme...
 my $tmp = scalar(@vol);
 print "Number of entries: $tmp \n"; # 1