I've started to draft a "macedir.org-based" spec for this. It is based on the IETF Internet-Drafts format in anticipation of future work. This approach (to reuse the I-D format) is common in the "open" standards game. The source is all up on github: https://github.com/leifj/macedir-entity-category. Here is how to produce html and txt version:

Get the xml from github and install the tool:

# apt-get install git-core xml2rfc
# git clone git://github.com/leifj/macedir-entity-category.git


# cd macedir-entity-category
# make
# less macedir-entity-category.txt