public function multipleOptions($field, array $options = [], $message = null, $when = null)
    {
        $extra = array_filter(['on' => $when, 'message' => $message]);
        $caseInsensitive = isset($options['caseInsensitive']) ? $options['caseInsensitive'] : false;
        unset($options['caseInsensitive']);

        return $this->add($field, 'multipleOptions', $extra + [
            'rule' => ['multiple', $options, $caseInsensitive]
        ]);
    }