public function additionalUserClass($additionalUserClass)
    {
        $additionalClasses = $this->getAdditionalUserClasses();
        
        if (($key = array_search($additionalUserClass, $additionalClasses)) !== false) {
            unset($additionalClasses[$key]);
        }
        
        $additionalClasses[] = $additionalUserClass;
        $this->setAdditionalUserClasses($additionalClasses);
    }