Class Reg_Polygon is defined in polygons.web, and
is derived from Polygon, using public derivation.
As noted above in Polygon Reference; Affine Transformations, class Reg_Polygon,
like class Rectangle,
currently inherits its transformation functions and
operator*=(const Transform&) from Polygon. Consequently,
the data members of a Reg_Polygon, except for center, are
not recalculated when it's transformed. I plan to change this soon! It
will also be necessary to add the function
Reg_Polygon::is_reg_polygonal(), in order to test whether a
Reg_Polygon is still regular and polygonal.