The "S" element can only follow a "C" or another "S" in the path definition.

The orange dot is the last point of the previous element and is the starting point for "S".

"S" is determined by 2 points.

The purple point directs the curvature of the path, together with the little grey point.

The pink point is the ending point of "S" and the starting point for the following element.

The grey point is determined by the position of the green dot. They are symmetrical in relation to the orange dot.

To see what I mean, move the green and purple dots.