public function additionalClass($additionalClass)
    {
        $additionalClasses = $this->getAdditionalClasses();
        
        if (($key = array_search($additionalClass, $additionalClasses)) !== false) {
            unset($additionalClasses[$key]);
        }
        
        $additionalClasses[] = $additionalClass;
        $this->setAdditionalClasses($additionalClasses);
    }