As long as I'm thinking about tangents... I just took derivative of existing curvePoint
equation and dumped it into curveTangent, here's a sample (stolen from the
bezierTangent sample) for the ref page if wanted:

stroke(0);
noFill();
curve(-200, 0, 10, 10, 90, 90, 500, 300);
stroke(255, 102, 0);
int steps = 16;
for (int i = 0; i <= steps; i++) {
float t = i / float(steps);
float x = curvePoint(-200, 10, 90, 500, t);
float y = curvePoint(0, 10, 90, 300, t);
float tx = curveTangent(-200, 10, 90, 500, t);
float ty = curveTangent(0, 10, 90, 300, t);
float a = atan2(ty, tx);
a -= PI/2.0;
line(x, y, cos(a)*8 + x, sin(a)*8 + y);
}

edit]
curveTangent() diff

oh that's super great, thanks so much!

i've added the patch for 0136.