code: public SVGPath relativeSmoothCubicTo(double c2x, double c2y, double x, double y) {
      return append(PATH_SMOOTH_CUBIC_TO_RELATIVE).append(c2x).append(c2y).append(x).append(y);
    }
docs: Smooth Cubic Bezier line to the given relative coordinates.
  
  @param c2x second control point x
  @param c2y second control point y
  @param x new coordinates
  @param y new coordinates
  @return path object, for compact syntax.