docs: def generate_excise_subparser(subparsers):
      """Adds a sub-command parser to `subparsers` to excise n-grams from
      witnesses."""
      parser = subparsers.add_parser(
          'excise', description=constants.EXCISE_DESCRIPTION,
          help=constants.EXCISE_HELP)
      parser.set_defaults(func=excise)
      utils.add_common_arguments(parser)
      parser.add_argument('ngrams', metavar='NGRAMS',
                          help=constants.EXCISE_NGRAMS_HELP)
      parser.add_argument('replacement', metavar='REPLACEMENT',
                          help=constants.EXCISE_REPLACEMENT_HELP)
      parser.add_argument('output', metavar='OUTPUT',
                          help=constants.EXCISE_OUTPUT_HELP)
      utils.add_corpus_arguments(parser)
      parser.add_argument('works', metavar='WORK',
                          help=constants.EXCISE_WORKS_HELP, nargs='+')