docs: def validate_options(self, k, v):
          """Validate options."""
  
          super().validate_options(k, v)
          if k == 'errors' and v.lower() not in ('strict', 'replace', 'ignore', 'backslashreplace'):
              raise ValueError("{}: '{}' is not a valid value for '{}'".format(self.__class__.__name, v, k))
          if k == 'normalize' and v.upper() not in ('NFC', 'NFKC', 'NFD', 'NFKD'):
              raise ValueError("{}: '{}' is not a valid value for '{}'".format(self.__class__.__name, v, k))