def gfftagstat_parser(subparsers):
    """
    Parser for the gfftagstat tool.
    """
    parser = subparsers.add_parser('gfftagstat', help=
        'get statistics on attribute tags of a GFF3 file', description=
        'Get statistics on attribure tags of a GFF file.')
    parser.add_argument('gff_file', help='a GFF3 file')
    parser.add_argument('-s', '--source', default=None, help=
        'filter GFF3 features by the specified source')
    parser.add_argument('-t', '--type', default=None, help=
        'filter GFF3 features by the specified type')
