docs: def set_option(prs, keyword, required=False):
      """Set options of command line.
  
      Arguments:
  
          prs:      parser object of argparse
          keyword:  processing keyword
          required: True is required option (default is False)
      """
      if keyword == 'server':
          prs.add_argument(
              '-s', dest='server', required=True,
              help='specify TonicDNS Server hostname or IP address')
  
      if keyword == 'username':
          prs.add_argument('-u', dest='username', required=True,
                           help='TonicDNS username')
  
      if keyword == 'password':
          group = prs.add_mutually_exclusive_group(required=True)
          group.add_argument('-p', dest='password',
                             help='TonicDNS password')
          group.add_argument('-P', action='store_true',
                             help='TonicDNS password prompt')
  
      if keyword == 'infile':
          prs.add_argument('infile', action='store',
                           help='pre-converted text file')
  
      if keyword == 'domain':
          prs.add_argument('--domain', action='store', required=True,
                           help='create record with specify domain')
          prs.add_argument('--name', action='store', required=True,
                           help='specify with domain option')
          prs.add_argument('--rtype', action='store', required=True,
                           help='specify with domain option')
          prs.add_argument('--content', action='store', required=True,
                           help='specify with domain option')
          prs.add_argument('--ttl', action='store', default='3600',
                           help='specify with domain option, default 3600')
          prs.add_argument('--priority', action='store', default=False,
                           help='specify with domain and '
                           'rtype options as MX|SRV')
  
      if keyword == 'update':
          prs.add_argument('--new-type', action='store',
                           help='specify new value with domain option')
          prs.add_argument('--new-content', action='store',
                           help='specify new value with domain option')
          prs.add_argument('--new-ttl', action='store',
                           help='specify new value with domain option')
          prs.add_argument('--new-priority', action='store',
                           help='specify new value with domain option')
  
      if keyword == 'template':
          msg = 'specify template identifier'
          if required:
              prs.add_argument('--template', action='store',
                               required=True, help=msg)
          else:
              prs.add_argument('--template', action='store',
                               help=msg)
  
      if keyword == 'search':
          prs.add_argument('--search', action='store',
                           help='partial match search or refine search.\
                           latter syntax is "name,rtype,content"')