The detection script is just a regular VBScript which can do almost everything a regular VBScript can do, including the regular If/Then, Do/Loop, For/Next, Subroutines, functions, and so on. It can only do almost everything because it still runs in the context of the browser, so this poses some limitations. For security purposes, the browser limits access to some local resources, so you won't be able to use objects, such as FileSystemObject. We can't list all the allowed or disallowed objects here, but when in doubt, simply experiment and see for yourself.
The detection script uses the Whale COM object, named after the original company that developed e-Gap, a product that preceded UAG by a few generations. This object has multiple methods, and yields an incredible amount of power. The full list of methods and collections is long, so we will focus on the more useful items. You can learn about the other items by reading the default detection...