def METHOD_NAME(parent_subparsers):
    """Add results subcommand."""
    main_parser = add_subcommand_parser(
        parent_subparsers, "results", description="Manipulate results"
    )
    main_subparsers = add_subparsers(main_parser, dest="subcommand")
    join = main_subparsers.add_parser("join", help="Join results")
    join.add_argument("results", help="Files with results", nargs="*", metavar="file")
    join.add_argument("output", help="Output file", metavar="output_file")
    if sys.version_info < (3, 8):
        join.register("action", "extend", ExtendAction)
    join.add_argument(
        "--prefixes",
        help="Add prefixes to result labels per file",
        action="extend",
        nargs="*",
        metavar="text",
    )
    join.add_argument(
        "--only",
        help="Select only results with matching label",
        metavar="label",
    )
    join.add_argument(
        "--re-label",
        help="Use prefixes as the new labels",
        action="store_true",
    )
    join.set_defaults(handler=join_results_cli)