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    Currently acceptable events are as follows:
 
  * Probe - probe is in the scene.* NoProbe - no probe is in the scene.
 * ProbeClose - probe is within the close tolerance to the current 
            feature specified by the VTV.
 * ProbeFar - probe is farther from the current feature than the close 
            tolerance specified by the VTV.
 * ProbeOnFeature - probe is on the feature (according to vision.)
 * ProbeNotOnFeature - probe is close, but not on the feature (according 
            to vision.)
 * VisionProblem - part string has changed, signifying that a feature 
            is occluded (need to move the camera.)
 * ProblemSolved - moving the camera has corrected the occlusion problem.
 * TouchedFeature - probe has touched the feature (according to touch 
            sensor,) feature is explored quantitatively and exact feature measurements 
            are taken in this state.
 * NoTouch - probe has not touched the feature (according to touch 
            sensor.)
 * ClosedRegion - current feature contains closed region(s) to be inspected 
            (recursively.)
 * OpenRegion - current feature contains open region(s) to be inspected 
            (iteratively.)
 * TimeOut - machine has not changed state within a period of time 
            specified by the VTV.
 * Done - inspection of the current feature and its children is complete, 
            return to previous level.
 
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