Outlines can be connected in several ways to form a single Outline. For example, a Fillet can connect two Outline Lines, to form one Outline made of three Outline Parts. Or an Outline Line can be connected to another Line by starting the Outline Line on the endpoint of the other Line. Or an Outline Line can start on the endpoint of an Outline Spline, to form a single Outline comprised of two Outline Parts. Since Outlines can be associated with only one Plane surface, you cannot connect two Outlines that are associated with different Planes (you will get a warning).