docs: def validate_bool(b):
      """Convert b to a boolean or raise"""
      if isinstance(b, six.string_types):
          b = b.lower()
      if b in ('t', 'y', 'yes', 'on', 'true', '1', 1, True):
          return True
      elif b in ('f', 'n', 'no', 'off', 'false', '0', 0, False):
          return False
      else:
          raise ValueError('Could not convert "%s" to boolean' % b)