The definition for PolygonCorners leaves much to be desired in terms of complexity.

The definition for PolygonCorners given in the document at the index https://developer.apple.com/documentation/roomplan/capturedroom/surface/polygoncorners.
Is woefully lacking. To validly link the sides of a polygon from the definition of a corner there needs to be an incoming and outgoing line descriptor that points to the next subsequent corner of the polygon. Just like a line has two endpoints, the edges of a polygon have corners to which any corner may be linked and it is an ordered set forwards and backwards, in the case of a 2D polygon. In the case of a 3D polygon, such a corner would likely have at the very least third directional connection giving depth of that point. In a 3D geometry you may have one point that has multiple points going in another direction much like the facet cuts of a Brilliant Cut Diamond. This sibling relationship of the corner points would complicate the definition but not impossibly so.