This site as was quickly recreated during August 2012 while YubNub was down, to provide most of its features. When YubNub came back up, it was more carefully redesigned to provide a similar but unique feature set.
There are two types of commands. The first is the substitution type, which supports most of YubNub's syntax, for simple operations. The other type is lua, which is able to execute entire programs written in the Lua programming language.
Queries are entered the same way regardless of the language their commands use. First is the command name (TODO: valid characters?), and then separated by spaces are the arguments. (TODO: quoted?) Named arguments can be specified with a single dash (TODO: example).
The substitution language is heavily based on the YubNub syntax in order to make switching practical. It is not yet thoroughly documented.
To learn the Lua language, the Lua users' wiki Tutorial Directory is quite helpful.