use strict;
use warnings;
use XML::LibXML;

my $file = 'n4000-small.xml';
my $parser = XML::LibXML->new();
my $doc = $parser->parse_file($file);

# THIS WORKS - but it's finding the vm node not the matrix node
foreach my $vm ($doc->findnodes('//vm[@type=\'br\']')) {
    print  "br  ", $vm->findvalue("./release/\@version"), "\n";
    if ( '7.2.1' eq $vm->findvalue("./release/\@version")) {
        print "found 7.2.2\n"
    }
}

# this also works, finding the "br" vm with the right version, but I think I need the matrix, to identify the "sns" vm

my @wanted_vm  = ($doc->findnodes('//vm[@type=\'br\' and ./release/@version=\'7.2.1\']'));
if( @wanted_vm ) {
    print "found br ", $wanted_vm[0]->findvalue('./release/@version'), "\n";
}

# this gets the 'br' matrices, but why doesn't it get the vm attributes?

foreach my $matrix ($doc->findnodes( '//matrix/vm[@type=\'br\']' )) {
    if( $matrix ) {
        #print "matrix:", $matrix->toString(), "\n";
        print "vm release version:", $matrix->findvalue('./vm/release/@version'), "\n";
        my $vm_type = $matrix->findvalue('./vm/@type');
        print "vm type:'" . $vm_type .  "'" . "\n";
    }
}