docs: def c_ls(api, args, verbose=False):
      """
  List bitstreams of an object::
  
      usage: cdstar ls [options] <URL>
  
      options:
          -t  sort by modification time, newest first
          -s  sort by filesize, biggest first
          -r  reverse order while sorting
  """
      obj = api.get_object(args['<URL>'].split('/')[-1])
      res = []
      for bitstream in obj.bitstreams:
          res.append((
              api.url(bitstream),
              bitstream._properties['content-type'],
              bitstream._properties['filesize'],
              datetime.fromtimestamp(bitstream._properties['last-modified'] / 1000.0)
          ))
      if args['-t']:
          res = sorted(res, key=lambda t: t[3], reverse=True)
      elif args['-s']:
          res = sorted(res, key=lambda t: t[2], reverse=True)
      if args['-r']:
          res = reversed(res)
  
      for r in res:
          yield '{0}\t{1}\t{2:>8}\t{3}'.format(*r) if verbose else r[0]