ambocc shader additional attributes? how?

[kensonuken]

I would like to add extra attributes like max error and bias etc... can anybody help me how to do that?

surface occsurf3(float samples = 64, maxdist = 1e30, coneangle = PI/2)

{

normal Ns = faceforward (normalize(N), I);

// Compute occlusion

float occ = occlusion(P, Ns, samples, "maxdist", maxdist, "coneangle", coneangle);

// Set Ci and Oi

Ci = (1 - occ) * Cs * Os;

Oi=Os;

}