code: func RegisterDataMatrix(pdf barcodePdf, code string) string {
  	bcode, err := datamatrix.Encode(code)
  	return registerBarcode(pdf, bcode, err)
  }
docs: // RegisterDataMatrix registers a barcode of type DataMatrix to the PDF, but not
  // to the page. Use Barcode() with the return value to put the barcode on the
  // page.