* crawler may only retrieve Sitemaps that were modified since a certain
     * date. This incremental Sitemap fetching mechanism allows for the rapid
     * discovery of new URLs on very large sites.
     */
    private String lastmod;

    /**
     * Creates a new SitemapFile instance.
     */
    public SitemapFile() {
        // Default constructor
    }

    /*
     * (non-Javadoc)

    /**
     * The priority of this URL relative to other URLs on your site. Valid
     * values range from 0.0 to 1.0. This value does not affect how your pages
     * are compared to pages on other sites—it only lets the search engines know
     * which pages you deem most important for the crawlers.
     *
     * The default priority of a page is 0.5.
     *