@DanRathbun From my point of view, my application reads a SUPolyline3dRef, and converts it as a polyline curve. Then in my application, I can treat it as a normal polyline curve, and have the special operation on the polyline curve.
You are correct: “The native Freehand Tool is not used much, so I think this is why you find it difficult to get models to test with.”.
@Wo3Dan With tt_su’s help, now I have learned how use Freehand Tool to create a model containing a SUPolyline3dRef( from the UI by holding down Shift while using the Freehand tool). That is what I want before.