code: func RegisterQR(pdf barcodePdf, code string, ecl qr.ErrorCorrectionLevel, mode qr.Encoding) string {
  	bcode, err := qr.Encode(code, ecl, mode)
  	return registerBarcode(pdf, bcode, err)
  }
docs: // RegisterQR registers a barcode of type QR to the PDF, but not to the page.
  // Use Barcode() with the return value to put the barcode on the page.
  //
  // The ErrorCorrectionLevel and Encoding mode are inherited from qr.Encode().