use XML::LibXML;

my $doc = XML::LibXML->load_xml(string => $xml);
my @mds = $doc->findnodes('//md');
for my $md ( @mds ) {
	my @mts = $md->findnodes('mi/mt');
	next unless @mts;
	my @rs = $md->findnodes('mi/mv/r');
	for my $i ( 0 .. $#mts ) {
		my ( $mt, $r ) = ( $mts[$i], $rs[$i] );
		print "mt: ", $mt->textContent, "\n";
		print "r: ", $r->textContent, "\n\n";
	}
}