Ho to use convertToNURBS

Hi,

since rel 4.9.4 it is available the function convertToNURBS, but the manual does not mention how to use it and what it does return (or I couldn't find it)

in my application I have several objects, some of them I will mesh with tetrahedra, others I would like to treat differently and it would helpful if I could get their NURBS representation, possibly one per each object,

is there any place in documentation where I could find this information?

I tried to make a sphere, convert to NURBS, and export to STEP, but the STEP file represent it as follows

#22 = SPHERICAL_SURFACE('',#23,1.);

and not as a NURBS (I would expect a set of bsplines objects and coefficients)

many thanks in advance, Andrea