protected function _addClass(FormHelper $formHelper, $options, $class)
    {
        $bootstrap = isset($options['bootstrap']) ? (bool)$options['bootstrap'] : true;
        if ($bootstrap) {
            $options = $formHelper->addClass((array)$options, $class);
        }

        if (isset($options['bootstrap'])) {
            unset($options['bootstrap']);
        }

        return $options;
    }