code: func (f *Fpdf) Rect(x, y, w, h float64, styleStr string) {
  	f.outf("%.2f %.2f %.2f %.2f re %s", x*f.k, (f.h-y)*f.k, w*f.k, -h*f.k, fillDrawOp(styleStr))
  }
docs: // Rect outputs a rectangle of width w and height h with the upper left corner
  // positioned at point (x, y).
  //
  // It can be drawn (border only), filled (with no border) or both. styleStr can
  // be "F" for filled, "D" for outlined only, or "DF" or "FD" for outlined and
  // filled. An empty string will be replaced with "D". Drawing uses the current
  // draw color and line width centered on the rectangle's perimeter. Filling
  // uses the current fill color.