XML::LibXML DTD Handling
This class holds a DTD. You may parse a DTD from either a string, or from an external SYSTEM identifier.
No support is available as yet for parsing from a filehandle.
XML::LibXML::Dtd is a sub-class of Node, so all the methods available to nodes (particularly toString()) are available to Dtd objects.
new 	

$dtd = XML::LibXML::Dtd->new($public_id, $system_id)

Parse a DTD from the system identifier, and return a DTD object that you can pass to $doc->is_valid() or $doc->validate().

 my $dtd = XML::LibXML::Dtd->new(
                      "SOME // Public / ID / 1.0",
                      "test.dtd"
                                );
 my $doc = XML::LibXML->new->parse_file("test.xml");
 $doc->validate($dtd);

parse_string 	

$dtd = XML::LibXML::Dtd->parse_string($dtd_str)

The same as new() above, except you can parse a DTD from a string.