docs: def _use_default(config_file):
      """Write default values to a config file. If another config file
      already exists, back it up before replacing it with the new file.
  
      :param config_file: `pathlib.Path` object. Path to config file.
      :return: `ConfigParser` object with the values loaded.
      """
      default_config = OrderedDict((
          (
              'gui',
              OrderedDict(
                  (
                      ('message_duration', 5),
                      ('gui_welcome_label', 'Welcome to the STEM Learning Center!'),
                      ('full_user_names', True),
                      ('large_font_size', 30),
                      ('medium_font_size', 18),
                      ('small_font_size', 15),
                      ('tiny_font_size', 10),
                      ('max_input_length', 9),
                  )
              ),
          ),
      ))
  
      parser = configparser.ConfigParser()
      parser.read_dict(default_config)
  
      if config_file.exists():
          backup = config_file.with_suffix('.bak')
          os.rename(str(config_file), str(backup))
          logger.info('{} moved to {}.'.format(config_file, backup))
  
      with config_file.open('w') as f:
          parser.write(f)
  
      logger.info('Default config file created.')
  
      return parser