code: func (f *Fpdf) Transform(tm TransformMatrix) {
  	if f.transformNest > 0 {
  		f.outf("%.5f %.5f %.5f %.5f %.5f %.5f cm",
  			tm.A, tm.B, tm.C, tm.D, tm.E, tm.F)
  	} else if f.err == nil {
  		f.err = fmt.Errorf("transformation context is not active")
  	}
  }
docs: // Transform generally transforms the following text, drawings and images
  // according to the specified matrix. It is typically easier to use the various
  // methods such as TransformRotate() and TransformMirrorVertical() instead.