BoxLinkDescription is ContactGeometryLinkDescription:
    .doc: """
Link description for a track belt with a contact_geometry with the shape of a box,
and possible variations in size given BoxLinkVariation type.
"""
    width is Real
    height is Real
    contact_geometry becomes Physics3D.Geometries.Box:
        size.y: width
        size.z: height
    variation becomes BoxLinkVariation
