From Vectorworks Developer
.VectorScript|VectorScript ..VS:Function Reference|Function Reference ..VS:Function_Reference_Appendix|Appendix
DescriptionAdds a Simple material to a Compound material. Sets the fraction of the Simple material as a relation to the whole. Fraction can have value between 0.0 and 1.0. "Primary" material is a simple material which carries the graphical attributes to be used by the compound material.
makePrimary :BOOLEAN) : BOOLEAN;
def vs.AddSubMtrlToMtrl(hMaterial, subMtrlName, fraction, makePrimary): return Boolean
hMaterial HANDLE Handle of a Compound material subMtrlName STRING Name of a Simple material to be added fraction REAL Fraction of the Simple material makePrimary BOOLEAN True if this Simple material should become the primary material of the Compound material