The points of a Polyline are retrieved and set by value; therefore new points are always copied in to the Polyline, not added directly. Polyline methods without a path index parameter work for both single part and multipart Polyline; if called on a multipart Polyline, methods without a path index work against the first path in the Polyline.

Note that the CoordinateSystem property of any new points added, inserted or set into existing an existing Polygon or Polyline will be discarded, and the coordinates (X and Y properties) of the point assumed to be in the same CoordinateSystem as the Polygon or Polyline to which they are added.