This seemed like the most logical place to mention this: It seems like the arrows in Fig. 58 in the online documentation for the buildmesh command are pointing in the wrong direction. The surface is supposed to be on the left of the boundary, but the arrows go clockwise around the perimeter. But shouldn’t they go counter-clockwise to define the surface to be inside the boundary as shown in Fig. 59?
I understand now: The C01-C06 border elements are plotted with negative arguments, reversing the orientation of the surface. The arrows go around clockwise, creating an exterior surface and are then reversed making it an interior surface.
The example is meant to illustrate how to create additional points to connect an interior border.
The extra wrinkle of reversing the orientation of the surface confused me, especially because the explanation of surface orientation comes immediately after this figure.