IfcPolynomialCurve is missing a clear definition

I think we should provide a short definition of a polynomial curve in IFC beyond `Polynomial Curve`.

How should the coefficients be applied? should it be:` IFCPOLYNOMIALCURVE([#], (0.0,1.0,3.14), [y], [z]) -> 0.0*x^0 + 1.0*x^1 + 3.14*x^2, y's, z's` which seems like to most logical

Should we assume any missing degree is 0? As expressed in a question from the [forum](https://forums.buildingsmart.org/t/ifcpolynomialcurve-clarification/4716):

> e.g. #7= IFCPOLYNOMIALCURVE(#4, (0.0,1.0), (0.0,0.0,-1.08943564E-04), $);
>
> Does this mean that when the number of elements in the lists is different then all lacking coefficients in the lesser list are equal to zero (in my example third element of the 'CoefficientX list)?

https://ifc43-docs.standards.buildingsmart.org/IFC/RELEASE/IFC4x3/HTML/lexical/IfcPolynomialCurve.htm