function update_results(){
    // Nonce check.
    $nonce = $_REQUEST['nonce'];
    if ( ! wp_verify_nonce( $nonce, 'ajax_search_filters_nonce' ) ) {
        die( __('Busted.') ); // Nonce check
    }

    // set is_search to true to that the results template can check it
    global $wp_query;
    $wp_query->is_search = true;

    $args = array();
    $args['s'] = $_REQUEST['search'];
    $args['post_type'] = array( 'news_article', 'perf_task', 'lesson_plan', 'diff_perf_task', 'diff_lesson_plan' );
    $args['post_status'] = 'publish';
    $args['tax_query'] = array( 'relation' => 'AND' );

    add_filter('posts_join', 'hsta_search_posts_join', 10, 2 );
    add_filter('posts_where', 'hsta_search_posts_where', 10, 2 );

    $meta_args = array(
        'relation' => 'OR',
        array(
            array(
                'key' => 'pt_assessment',
                'value' => 'rebel',
                'compare' => 'LIKE'
            ),
        ),
        array( 'relation' => 'AND' ),
    );

    // collect filter data
    // apply post types
    if ( array_key_exists( 'types', $_REQUEST ) && is_array( $_REQUEST['types'] ) && count( $_REQUEST['types'] ) > 0 ) {
        $args['post_type'] = $_REQUEST['types'];
    }

    // apply grade filter (if any)
    if ( array_key_exists('grade', $_POST) && strlen( $_POST['grade'] ) > 0 ) {
        $meta_args[1][] = array(
            'key' => 'pt_grade_level',
            'value' => $_POST['grade'],
            'compare' => '=',
        );
    }

    // apply content area filter (if any)
    if ( array_key_exists('contentArea', $_POST) && strlen( $_POST['contentArea'] ) > 0 ) {
        $meta_args[1][] = array(
            'key' => 'pt_content_area',
            'value' => serialize( strval( $_POST['contentArea'] ) ),
            'compare' => 'LIKE',
        );
    }

    // apply standard filter (if any)
    if ( array_key_exists('standard', $_POST) && strlen( $_POST['standard'] ) > 0 ) {
        $meta_args[1][] = array(
            'key' => 'pt_standard',
            'value' => $_POST['standard'],
            'compare' => '=',
        );
    }

    // apply PD Course taxonomy filter (if any)
    if ( array_key_exists('pdCourse', $_POST) && strlen( $_POST['pdCourse'] ) > 0 ) {
        $args['tax_query'][] = array(
            'taxonomy' => 'pd_courses',
            'field' => 'id',
            'terms' => $_POST['pdCourse'],
            'operator' => 'IN',
        );
    }

    $meta_loop = new WP_Meta_Query( $meta_args );
    global $wpdb;
    $GLOBALS['meta_sql'] = $meta_loop->get_sql('post', $wpdb->posts, 'ID', $context = null );
    $loop = new WP_Query( $args );
    ob_start(); ?>
    <hr>
    <h1>Ajax Results</h1>
    <?php
    if ( ! $loop->have_posts() ) {

    }

    // render results
    while ( $loop->have_posts() ) : $loop->the_post(); ?>
        <?php
            global $post;
            setup_postdata( $post );
        ?>
        <?php get_template_part( 'templates/results', 'search' ); ?>
    <!-- hsta_the_task_perf_card( $post ); -->
    <?php endwhile;
    wp_reset_postdata();

    $return = ob_get_contents();
    ob_end_clean();

    wp_send_json_success( $return );
}
add_action( 'wp_ajax_update_results', 'update_results' );
add_action( 'wp_ajax_nopriv_update_results', 'update_results' );

// filter
function hsta_search_posts_join( $join ) {
    $join .= $GLOBALS['meta_sql']['join'];
    return $join;
}
function hsta_search_posts_where( $where, $wp_query ) {
    $re = "/^ AND/";
    $subst = " OR";
    $meta_where = preg_replace($re, $subst, $GLOBALS['meta_sql']['where']);
    $where .= $meta_where;
    return $where;
}