You've coded the features for sub/sup haven't you?

Ooops, double post. Apologies

I guess I haven't coded those features... any recommended tutorial for an absolute newbie in OpenType coding?

You can copy the code from fonts which have it.
It’s not copyrighted.

Whether or not any particular code is copyrighted, without the source file you're gonna be looking at decompiled code, which can be tricky to decipher. Even the FreeFontPro VFB source file provided with FontLab has a dizzying array of class substitutions.

Here's what a basic, bare-bones sups feature might look like in FL.

Note that the classes here are defined in the OpenType panel for clarity (with some extra line breaks), but they could just as well be made in the Classes panel.

any recommended tutorial for an absolute newbie in OpenType coding?

This article on OpenType substitution features at I Love Typography covers quite a bit while managing to stay newbie-friendly.

Thanks a lot Nick and gargoyle!

Not newbie-friendly:
http://www.adobe.com/devnet/opentype/afdko/topic_feature_file_syntax.html
http://ansuz.sooke.bc.ca/entry/131