code: def _register_opt(parser, *args, **kwargs):
          
          try:
              # Flake8 3.x registration
              parser.add_option(*args, **kwargs)
          except (optparse.OptionError, TypeError):
              # Flake8 2.x registration
              parse_from_config = kwargs.pop('parse_from_config', False)
              option = parser.add_option(*args, **kwargs)
              if parse_from_config:
                  parser.config_options.append(option.get_opt_string().lstrip('-'))
docs: Handler to register an option for both Flake8 3.x and 2.x.
  
          This is based on:
          https://github.com/PyCQA/flake8/blob/3.0.0b2/docs/source/plugin-development/cross-compatibility.rst#option-handling-on-flake8-2-and-3
  
          It only supports `parse_from_config` from the original function and it
          uses the `Option` object returned to get the string.