feed rewrite

// === on init: ===
    foreach (self::$CUSTOM_FEEDS as $custom_feed)
    {
        //add_feed( $custom_feed, array($class, $custom_feed) );
        $hook = "do_feed_$custom_feed";
        remove_action($hook, $hook, 10, 1);
        add_action( $hook, array($class, $custom_feed), 10, 1 );
        add_filter( "generate_rewrite_rules", array($class, "{$custom_feed}_rewrite") );
    }
    add_action( 'admin_init', 'flush_rewrite_rules' );



// === rewrite rules ===
    static function customfeed_rewrite( $wp_rewrite )
    {
        $feed_name = str_replace(__FUNCTION__, '_rewrite', '');
        $feed_rules = array(
            "feed/$feed_name/(.*)" => "index.php?feed=$feed_name&parent_id=" . $wp_rewrite->preg_index(1),
        );

        $wp_rewrite->rules = $feed_rules + $wp_rewrite->rules;
        $wp_rewrite->flush_rules();
    }