xAPPWINDOW   Variable

Variable   : The name of the variable where the names of any files whose 
           icons were dropped into the AppWindow will be placed.

When you declare this event, you also make the window an AppWindow.
No other action is needed.

An AppWindow can not (currently) be switched ON or OFF.

Only one xAppWindow event can be declared per GUI. 
If you declare 2, the 2nd one will be disregarded.