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.