private function getPortableElementSubclasses($superClassName){
        $subClasses = [];
        foreach(PortableModelRegistry::getRegistry()->getModels() as $model){
            $portableElementClass = $model->getQtiElementClassName();
            if(is_subclass_of($portableElementClass, $superClassName)){
                $subClasses[] = $portableElementClass;
            }
        }
        return $subClasses;
    }