extending Xpath

Hi,
I was wondering if it was possible to extend the DOMXpath object in a
similar fashion to the DomDocument.

I was hoping to write a wrapper to provide an interface similar to
prepared statements in the db libraries for the xpath processor.


$xpath = new myxpath();

$stmt = $xpath->prepare("/foo/bar[@foo = '?' ]");
$stmt->bindParam( '?', $potentiallynastystring );
$x = $stmt->execute();

I have tried :

final class timber_utils_domxpath extends DomXpath
{
   public function __construct( DOMDocument $dom )
   {
       echo "in here";
       parent::_construct( $dom );
   }
}


but I get the following error
Fatal error: Call to undefined method DOMXPath::_construct()

Many thanks
Andrew