Just to point out an alternative. I presume you want to use XML::Checker to validate the XML against a DTD and not just see if the XML itself is valid. If that's the case, XML::LibXML is a fine alternative. I use it in production code to validate XML against DTDs.

my $parser = XML::LibXML->new;
$parser->validation(1);
eval { $doc = $parser->parse_string($xml); };
if ($@) {
   # XML not well formed, error handling here...
}
eval { $doc->validate; };
if ($@) {
   # XML did not pass DTD validation, error handling here...
}
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