docs: def val_to_mrc(code, val):
      """
      Convert one single `val` to MRC.
  
      This function may be used for control fields in MARC records.
  
      Args:,
          code (str): Code of the field.
          val (str): Value of the field.
  
      Returns:
          str: Correctly padded MRC line with field.
      """
      code = str(code)
      if len(code) < 3:
          code += (3 - len(code)) * " "
  
      return "%s   L %s" % (code, val)