You can use subapplications for two purposes:

You create a subapplication by adding it to an existing application edition.

Because a subapplication exists within another application, it cannot specify prerequisites. A subapplication must inherit prerequisites from its containing (or root) application. Further, it cannot itself be a prerequisite.

A subapplication has the same scope as its application. This means that a subapplication can use any class or method defined by the application or any other subapplication inside the application. The exception to this is private classes. Private classes can be used only within the scope of the defining application or subapplication.

A subapplication can contain subapplications.