* both sources differently.
     */
    private String lastmod;

    /**
     * How frequently the page is likely to change. This value provides general
     * information to search engines and may not correlate exactly to how often
     * they crawl the page. Valid values are:
     * <ul>
     * <li>always</li>
     * <li>hourly</li>
     * <li>daily</li>