* 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>
     * <li>weekly</li>
     * <li>monthly</li>
     * <li>yearly</li>
     * <li>never</li>
     * </ul>
     * The value "always" should be used to describe documents that change each