It doesn't handle higher order NURBS or use knots. It's just the basics, but there are a lot of geometric algorithms in there. We're still trying to get the bugs out of NURBS booleans, but the high level algorithm is sound.
BTW it can also be compiled for web but that is incomplete.
Probably the most accessible NURBS kernel to learn from is the one in Solvespace. The entire source for the core NURBS is about 6KLoC:
https://github.com/solvespace/solvespace/tree/master/src/srf
My favorite file in there is ratpoly.cpp
It doesn't handle higher order NURBS or use knots. It's just the basics, but there are a lot of geometric algorithms in there. We're still trying to get the bugs out of NURBS booleans, but the high level algorithm is sound.
BTW it can also be compiled for web but that is incomplete.