domXML - how to add DTD

[kolcun]

I was wondering if anyone knows how to add a DTD specification like to the xml objet?

ie.. the like of code $doc = new_xmldoc('1.0');
corresponds to <?xml version="1.0" ?> in the xml file

I need the PHP code to add the DTD line
<!DOCTYPE calendarXMLnodes SYSTEM "calendar.dtd"

anyone know how to do such a thing?

thanks a lot
/mike