public function loadXml( $xml )
	{
		$this->document	= new DOMDocument();
		$validator	= new XML_Validator();
		if( !$validator->validate( $xml ) ){
			$message	= $validator->getErrorMessage();
			throw new InvalidArgumentException( 'XML is invalid ('.$message.')' );
		}
		$this->document->loadXml( $xml );
		$this->xPath	= new DOMXPath( $this->document );
	}