Some web sites have multiple copies of the same content accessed via different URLs. Often, these sites will indicate the preferred version of the content by including a special tag indicating the canonical URL. Sitemap Creator can optionally honor such preferences, and automatically ignore non-canonical URLs.
To enable or disable canonical URL support:
When the option is set, any URL which contain a canonical URL declaration in the page header will be included in the sitemap as normal. If a canonical URL declaration is present however, the URL will be automatically excluded from the site map unless it matches the canonical URL.