This is the companion wiki for machinetags.org, a place to document implementations, namespaces, machine tag theory, or whatever other machine taggy bits might catch your fancy.
Machine tags are a form of tag that add semantic structure to tagging in a way both readable to humans and computers. Also known as “triple tags”, they originated in the geohacking community as a way to encode latitude/longitude data in tag systems like http://del.icio.us and http://flickr.com.
Checkout the namespace page, and the predicate page for a list of machine tags known to be in use. Machine tags, like all tags, tend to conform to only a rough organizational and adhoc structure, so this list will never be complete or definitive.
The support for structured tags accross Web sites varies very much. This is a list of sites and programs that make use of structured tags