Comprehensive List of All Tags?

Is there a comprehensive list of all tags/variables (ie. $left, $mid, $len) and what they do? I've done a search but could not find any.

Thanks!

What search did you do?

Open Mp3tag, press key [F1] and begin reading ... you will find the next branch to the scripting language functions and other stuff immediately.

Online help is there:
http://help.mp3tag.de/

DD.20100429.0753.CEST