``True`` if values of all config items in this section and its subsections
        have their values equal to defaults or have no value set.

def is_default(self):
        """
        ``True`` if values of all config items in this section and its subsections
        have their values equal to defaults or have no value set.
        """
        for _, item in self.iter_items(recursive=True):
            if not item.is_default:
                return False
        return True