my $text = q|<?xml version="1.0" encoding="UTF-8"?>
<TMSMessage xmlns="http://xmlns.sony.net/d-cinema/tms-api/v1">
<MessageHeader>
<Id>-1</Id>
<Type>ListPerformances</Type>
...etc
</TMSMessage>|;

my $doc = XML::LibXML->load_xml(string => $text);
my $xc = XML::LibXML::XPathContext->new( $doc->documentElement() );
$xc->registerNs( pfx => 'http://xmlns.sony.net/d-cinema/tms-api/v1' );

my @events = $xc->findnodes('//pfx:EventInfo');
for my $event (@events) {
	my $id = $xc->findvalue('pfx:EventId', $event);
	print "EventId: $id\n";
	my @packs = $xc->findnodes('pfx:PreshowPackList/pfx:PreshowPack', $event);
	if ( not @packs ) {
		print "No Packs\n";
		next;
	}
	for my $pack (@packs) {
		my $pack_id = $xc->findvalue('pfx:PackId', $pack) || "No PackId";
		print "PackId: $pack_id\n";
	}
}