code: def main():
      
      parser = argparse.ArgumentParser(description=__doc__)
      parser.add_argument(
          '--boost_dir',
          required=False,
          type=existing_path,
          help='The path to the include/boost directory of Metaparse'
      )
      parser.add_argument(
          '--max_length_limit',
          required=False,
          default=2048,
          type=positive_integer,
          help='The maximum supported length limit'
      )
      parser.add_argument(
          '--length_limit_step',
          required=False,
          default=128,
          type=positive_integer,
          help='The longest step at which headers are generated'
      )
      args = parser.parse_args()
  
      if args.boost_dir is None:
          tools_path = os.path.dirname(os.path.abspath(__file__))
          boost_dir = os.path.join(
              os.path.dirname(tools_path),
              'include',
              'boost'
          )
      else:
          boost_dir = args.boost_dir
  
      if args.max_length_limit < 1:
          sys.stderr.write('Invalid maximum length limit')
          sys.exit(-1)
  
      generate_string(
          os.path.join(
              boost_dir,
              'metaparse',
              'v{0}'.format(VERSION),
              'cpp11',
              'impl'
          ),
          length_limits(args.max_length_limit, args.length_limit_step)
      )
docs: The main function of the script