I just finished moving the APE tags specifications from Frank Klemm's original pages.
The more obvious advantage to that is that the specs can now receive contributions from everyone. The less obvious advantage is that people are now freed from Klemm's webdesign and animated GIFs
Some parts that could receive contributions are the list of APE keys (http://wiki.hydrogenaudio.org/index.php?title=APE_key) and the Label Code (http://wiki.hydrogenaudio.org/index.php?title=APE-LC) list (although I wonder about its usefulness).
When editing the APE keys, please use common sense. I think we can all agree we don't need a field "Brand and model of microphone used by performer"
Late response but thank you!
Personally I do think it would be usefull to have a label code list. Especially for using it in tags.
I'll try to find some resources to compile a bigger list.