[ic] Variables - Locations?

[interchange-users@interchange.redhat.com (Matt)]

I am working through editing things like my theme.cfg file and I am 
curious what file includes what each variable is assigned to?

For example:

Variable  THEME_LOGO     __THEME_IMG_DIR__/logo.gif

Where would I find what __THEME_IMG_DIR__ is equal to?

Also,... can someone post a link to any good documentation on 
Interchange that exists?  So far I'm not finding much of anything.

Thank You