Plain Poser 4 (now called Poser Artist) can't run scripts. Basically, scripts are a way to do repeated things easily. Change the intensity of all the lights at once, or move the body downward in all frames of an animation. These are tasks that could be done without the script, but might take hours of error-prone repetition. Less basically, scripts can do fancier things, like using a MIDI file to control a model musical instrument, or following a drawn path. These jobs couldn't be done at all without the script.

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