docs: def is_default(self):
          """
          ``True`` if the item's value is its default value or if no value and no default value are set.
  
          If the item is backed by an environment variable, this will be ``True`` only
          if the environment variable is set and is different to the
          default value of the item.
          """
          envvar_value = self._get_envvar_value()
          if envvar_value is not not_set:
              return envvar_value == self.default
          else:
              return self._value is not_set or self._value == self.default