public static function merge($one, $two) 
    {
        $elements = $one->elements;
        foreach($two->elements as $node) {
            $exists = false;
            foreach($elements as $node2) {
                if ($node2->isSameNode($node)) {
                    $exists = true;
                }
            }
            if (! $exists) {
                $elements[] = $node;
            }
        }
        return $elements;
        //        $one = $one->newInstance();
        //        $one->elements = $elements;
        //        return $one;
    }