why is documentation needed???
I once thought the same, but I discovered that it will not have any use as you can find all the tags at the default templates. Also do many MODS add some more tags. As it is not possible to use all tags at all templates, it will be lots of work to make a document in which you discribe what tags are useful for which templates, but by just looking at the default templates you will be able to find all tags you need.
Cheers,
Vraxor