The class ArcDirected is used where some kind of movement or direction exists along or across the arc. A value of forward for direction implies movement from the first point in the list of points defining position to the last point, either directly on the arc or along one or both sides of the arc. Besides forward, backward, bothDirections, noDirection and unknown, the value of direction may be specified as across, acrossLeftToRight, and across RightToLeft. These last three options imply movement crossing the arc, instead of along the arc. Right and left are with respect to a traverse along the arc from the first point to the last point in the list of points. If direction is unspecified, it is assumed that it is forward.