This is a deprecated repository containing older versions of the HED schema (in wiki format). The site has been superceded by https://github.com/hed-standard. The new site consolidates all of the HED information from different sources.
For the HED schema please visit: https://github.com/hed-standard/hed-specification/wiki.
For more general information regarding HED please visit: http://www.hedtags.org. The associated github site contains all of the tools including links to documentation, publications and the online validator.