Hi Rob, unfortunately I don't currently have any proper documentation available for doing that...

Basically right now you've just got to study existing commands and scripts, and try things out.

A couple of resources:

http://moi3d.com/wiki/Scripting - get the moi.idl file from here where you can see a listing of the various properties and methods that are available to a script.

And Petr's MoI page here:
http://kyticka.webzdarma.cz/3d/moi/

has a collection of a variety of different scripts and custom commands that have been gathered from prior discussions in the forum here.

If you look over that stuff you can kind of see what stuff is available for a script to do.

Also commands are actually implemented in script as well, you can check out the script file for commands in the \commands sub-folder inside of MoI's main installation folder, so that is another source of examples to study.

The script language used is JavaScript, and you should be able to find quite a few tutorials online for how that language itself works, since it is the script language that is used inside of web pages.

- Michael