The main source file for a VTS application is called "AppMod.src", and is stored in the application's directory. The AppMod.src root file is the main application module file listing all top-level variables and modules for the application. Without going into too much technical detail for VTS developers who are not familiar with programming and VTS scripting terminology, the AppMod.src file is like a directory of all the code files that will be used for the application. This file is therefore crucial for each application and must never be deleted.