public static function getRadioButtonErrorSelector($formName, $fieldSetIndex)
    {
        $fieldSetSelector = CssSelector::getFieldSetByIndexSelector($formName, $fieldSetIndex);

        if (empty($fieldSetSelector)) {
            return '';
        }

        $errorContainerSelector = static::getFieldErrorContainerSelector();

        return sprintf('%s legend.col-form-label %s', $fieldSetSelector, $errorContainerSelector);
    }