Validation of XML Schemas is covered in the Perl XML FAQ

use XML::LibXML;

my $schema_file = 'po.xsd';
my $document    = 'po.xml';

my $schema = XML::LibXML::Schema->new(location => $schema_file);

my $parser = XML::LibXML->new;
my $doc    = $parser->parse_file($document);

eval { $schema->validate($doc) };
die $@ if $@;

print "$document validated successfully\n";
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You may need to update the libxml2 library on your system if it is quite old (and then rebuild XML::LibXML::Common and XML::LibXML)