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It's easy to launch a non-scriptable application but difficult to easily do anything too productive with it. Consider the following line:
tell application "SimpleText" to activate
This will launch "Simple Text" but having it do anything afterward would require scripting additions. A free Scripting Addition called S√?¬§ndi's Additions allows text to be typed, so we could do something like:
tell application "SimpleText"
To choose from menus, access dialog boxes, and do more would require other additions, or an all-in-one extension called PreFab Player.
In general, non-scriptable applications are cumbersome to deal with and more often than not a scriptable equivalent can be found; in this case the $15 shareware text editor Tex-Edit Plus is highly scriptable and offers other features Simple Text can only dream about!