Script Debugger lets you set another script as the implicit parent of the current script (using AppleScript’s script object inheritance mechanism). Both scripts must be open. Then:

• Bring the “child” script frontmost and choose Script > Parent Script and the name of the parent script. (You can also add a Parent Script popup menu to the script window’s toolbar.)

This parent-child relationship persists only while both scripts are open. If you try to close the parent script, you’ll get a dialog warning that you’re about to break the parent-child relationship.

This feature is useful for testing individual handlers in a script without altering that script. It can be employed to make a set of top-level entities (properties, handlers, etc.) from one script available in another, or for simulating a runtime environment where such parent script relationships are used.