At intervals set by the SequenceFrameRate property, FrameToDisplay steps backwards by SequenceStepCount frames. If a step of SequenceStepCount frames would go beyond the SequenceFrameRange, then the SequenceEndBehavior property is consulted to determine if the playback should stop, loop or reverse direction.
If this McView instance is the McWindow.View property of the McApplication.ActiveWindow, then the ImageToDisplay.ActiveFrameIndex will follow the displayed FrameToDisplay.