Nonlinear Grey Box Modeling code - idnlgrey algorithm

I'm wondering if you would let me know whats the algorithm behind idnlgrey model? Is it based on polynomial nonlinear state space model or extended kalman filter method or other method? Whats the advantage of idnlgrey rather that EKF method for solving nonlinear state space models?

[Florian Anderl]

I wonder about the same question. I cannot find this information anywhere...