docs: def list():
      """
      List available format.
      """
      choice_len = max(map(len, _input_choices.keys()))
      tmpl = "  {:<%d}: {}\n" % choice_len
      text = ''.join(map(
          lambda k_v: tmpl.format(k_v[0], k_v[1][0]), six.iteritems(_input_choices)))
      click.echo(text)