With this code, we can add new fields. 

We would like to know how to indicate that these new fields are mandatory. 
Also know, how to make the fields that are already in the form, 
mandatory or optional.

Thank you in advance. Great plugin!

/**
 * This code adds two custom fields (text input and select element) on the front-end modal window
 */
add_action('wp_footer', function() {
    ?>
    <script type="text/javascript">
        (function ($) {
            $(document).on('stecOnRsvpAfterFields', function (e, data) {
                var customHtml = [
                    '<input type="text" name="attendee_country" placeholder="Country" />',
                    '<select name="attendee_tag"><option value="1">Tag</option></select>'
                ];
                data.temp.customFields = customHtml;
            });
        })(window.jQuery);
    </script>
    <?php
});-->