To be complete, ARexx scripts should be able to do everything a user can do in your application. See everything for details.
Most applications don't themselves provide any way for the user to change the size or position of a window, but allow intuition to provide that facillity. Providing ARexx scripts with that facility - especially in server mode - allows the display of your application to be better integrated into multi-application presentation systems.
It may be usefull to provide facilities to an ARexx interface that aren't available to the user at the keyboard. Locking out the keyboard, or some set of commands, or a terminal emulator allowing a script to wait for some string from the serial port.
The ability to make sure the scripts and the user don't interere with each other is critical. A special "server" mode, where the application runs without ever opening a window, can be especially usefull.
On to well defined, or up to goals of a design.
Mike W. Meyer