def add_arguments_rnn_decoder_common(group):
    """Define common arguments for RNN decoder."""
    group.add_argument(
        "--dtype",
        default="lstm",
        type=str,
        choices=["lstm", "gru"],
        help="Type of decoder network architecture",
    )
    group.add_argument(
        "--dlayers", default=1, type=int, help="Number of decoder layers"
    )
    group.add_argument(
        "--dunits", default=320, type=int, help="Number of decoder hidden units"
    )
    group.add_argument(
        "--dropout-rate-decoder",
        default=0.0,
        type=float,
        help="Dropout rate for the decoder",
    )
    group.add_argument(
        "--sampling-probability",
        default=0.0,
        type=float,
        help="Ratio of predicted labels fed back to decoder",
    )
    group.add_argument(
        "--lsm-type",
        const="",
        default="",
        type=str,
        nargs="?",
        choices=["", "unigram"],
        help="Apply label smoothing with a specified distribution type",
    )
    return group