A parametric point is stored in the go_parametric_point structure.
It has a curve anchor and a “parameter” property which expresses the parameter
of the point position on the curve. It has one hanger for the point position.
The type is GOT_PARAMETRIC_POINT and the subtype is GOST_PARAMETRIC_POINT.
The parametrization is linear; the parameter value grows linearly along the curve.