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   High-level airship design tool.
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   Form:
   tag = AirshipDesignGUI( action, modifier )
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   Inputs
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   action          (1,:)   Action to be taken by the Airship Design GUI
   modifier        (:)     Modifier applied to action
   data            (:)     Data passed

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   Outputs
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   tag             (1,:)   Returns the window tag on initialization

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