Enable the automatic generation of sitemap.xml from existing HTML by specifying a minimal amount of semantic information.
Countless sites contain HTML navigation constructs which already detail parts of the information required to build a sitemap file. Typically these constructs leverage link elements which conveniently expose an 'href' attribute. Add a way to specify 'priority' and maybe 'changefreq' and enough would be in place for machines to build a site map.
Currently the alternative is to either write a site map manually, or supply information to a generator (the said data being disconnected from your site).
The sitemap protocol is very simple.
Per the microformats The microformats process: