def subparser(subparsers):
    """Define the `kevlar localize` command-line interface."""
    desc = """    For each partition, compute the reference target sequence to use for
    variant calling. NOTE: this command relies on the `bwa` program being in
    the PATH environmental variable.
    """
    subparser = subparsers.add_parser('localize', description=desc)
    subparser.add_argument('-d', '--delta', type=int, metavar='Δ', default=
        50, help=
        'retrieve the genomic interval from the reference by extending beyond the span of all k-mer starting positions by Δ bp'
        )
    subparser.add_argument('-p', '--part-id', type=str, metavar='ID', help=
        'only localize partition "ID" in the input')
    subparser.add_argument('-o', '--out', metavar='FILE', default='-', help
        ='output file; default is terminal (stdout)')
    subparser.add_argument('-z', '--seed-size', type=int, metavar='Z',
        default=51, help='seed size; default is 51')
    subparser.add_argument('-x', '--max-diff', type=int, metavar='X',
        default=None, help=
        'split and report multiple reference targets if the distance between two seed matches is > X; by default, X is set dynamically for each partition and is equal to 3 times the length of the longest contig in the partition; each resulting bin specifies a reference target sequence to which assembled contigs will subsequently be aligned'
        )
    subparser.add_argument('--include', metavar='REGEX', type=str, help=
        'discard alignments to any chromosomes whose sequence IDs do not match the given pattern'
        )
    subparser.add_argument('--exclude', metavar='REGEX', type=str, help=
        'discard alignments to any chromosomes whose sequence IDs match the given pattern'
        )
    subparser.add_argument('refr', help='BWA indexed reference genome')
    subparser.add_argument('contigs', nargs='+', help=
        'assembled reads in augmented Fasta format')
