code: def _check_d1_characters(name):
      # type: (bytes) -> None
      '''
      A function to check that a name only uses d1 characters as defined by ISO9660.
  
      Parameters:
       name - The name to check.
      Returns:
       Nothing.
      '''
      bytename = bytearray(name)
      for char in bytename:
          if char not in _allowed_d1_characters:
              raise pycdlibexception.PyCdlibInvalidInput('ISO9660 filenames must consist of characters A-Z, 0-9, and _'f _check_d1_characters(name):
      # type: (bytes) -> None
      '''
      A function to check that a name only uses d1 characters as defined by ISO9660.
  
      Parameters:
       name - The name to check.
      Returns:
       Nothing.
      '''
      bytename = bytearray(name)
      for char in bytename:
          if char not in _allowed_d1_characters:
              raise pycdlibexception.PyCdlibInvalidInput('ISO9660 filenames must consist of characters A-Z, 0-9, and _')
docs: A function to check that a name only uses d1 characters as defined by ISO9660.
  
      Parameters:
       name - The name to check.
      Returns:
       Nothing.