On program startup, default.lua is called in here. These scripts are vital to the plugin -- DO NOT MODIFY them if you don't know what the hell you're doing! In fact, it'd be a good idea not to modify them at all...
A couple of undocumented system variables and functions are used in these scripts. I'll answer any questions you have about them, but you really don't NEED to know what they are, hence the undocumentation.