I'm trying to extend the DOMDocument class so as to make XPath selections easier. I wrote this piece of code:

class myDOMDocument extends DOMDocument {

 function selectNodes($xpath){
   $oxpath = new DOMXPath($this);
    return $oxpath->query($xpath);
  }

  function selectSingleNode($xpath){
   return $this->selectNodes($xpath)->item(0);
  }
}

These methods return a DOMNodeList and a DOMNode object, respectively. What I'd like to do now is to implement similar methods to the DOMNode objects. But obviously if I write a class (myDOMNode) that extends DOMNode, I won't be able to use these two extra methods on the nodes returned by myDOMDocument because they're DOMNode (and not myDOMNode) objects.

I'm rather a beginner in object programming, I've tried various ideas but they all lead to a dead-end.

Any hints? Thanks a lot in advance.