def add_args(parser):
        """Add criterion-specific arguments to the parser."""
        # fmt: off
        parser.add_argument(
            '--label-smoothing',
            default=0.,
            type=float,
            metavar='D',
            help='epsilon for label smoothing, 0 means no label smoothing')
        # fmt: on
Add criterion-specific arguments to the parser.
infoxlm/fairseq/fairseq/criterions/nat_loss.py