code: func (f *Fpdf) TransformSkew(angleX, angleY, x, y float64) {
  	if angleX <= -90 || angleX >= 90 || angleY <= -90 || angleY >= 90 {
  		f.err = fmt.Errorf("skew values must be between -90° and 90°")
  		return
  	}
  	x *= f.k
  	y = (f.h - y) * f.k
  	var tm TransformMatrix
  	tm.A = 1
  	tm.B = math.Tan(angleY * math.Pi / 180)
  	tm.C = math.Tan(angleX * math.Pi / 180)
  	tm.D = 1
  	tm.E = -tm.C * y
  	tm.F = -tm.B * x
  	f.Transform(tm)
  }
docs: // TransformSkew generally skews the following text, drawings and images
  // keeping the point (x, y) stationary. angleX ranges from -90 degrees (skew to
  // the left) to 90 degrees (skew to the right). angleY ranges from -90 degrees
  // (skew to the bottom) to 90 degrees (skew to the top).
  //
  // The TransformBegin() example demonstrates this method.