PHP5: ext/dom - set namespace of node manually

Hello,
the following code shows my problem:

<?php
        class MyElement extends DomElement {
                function __construct($name) {
                        parent::__construct($name);
                }
        }
        
        $doc = new DomDocument();
        
        $node = new MyElement("test");
        $node = $doc->appendChild($node);
        $node->setAttribute("xmlns", "http://www.somedomain.de/");
        
        print("Namespace: '" . $node->namespaceURI . "'");
        
        $xmlCode = $doc->saveXML();
        print("<pre>" . htmlspecialchars($xmlCode) . "</pre>");
?>

the output would be:
> Namespace: ''
> <?xml version="1.0"?>
> <test xmlns="http://www.somedomain.de/"/>

As you can see it is impossible to set the namespace manually! I tried to
set it with the help of a DomNamespaceNode-object but those objects are no
"real" nodes (why!?!) and the consequence is that you couldn't append such
a node with $node->appendChild($domnamspacenode_object); ...

Further it isn't possible to use the function $doc->createElementNS(...)
because this function returns a domelement-object but i want the element to
be my own MyElement-object.

So how to get a namespace in my node???

thanks in advance,

vivi