!DOCTYPE creation viadom implementation

I'm having a hard time creating the !DOCTYPE instruction. As far as i
know i need to use the domimplementation approach, but if there is some
other way I'd like to hear it. Here is my code:

<?php
$doctype=domImplementation::createDocumentType("html",
"-//W3C//DTD XHTML 1.0 Transitional//EN",
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd");
$docRoot=domImplementation::createDocument('http://www.w3.org/1999/xhtml','html:html',$doctype);
$docRoot->encoding='utf-8';
print($docRoot->saveXML());
?>

My current workaround is importing a "stub" document containing
everything i want, but that is not really satisfactory...

/Jaanus