code: def register_multi_flags_validator(flag_names,
                                     multi_flags_checker,
                                     message='Flags validation failed',
                                     flag_values=FLAGS):
    
    v = gflags_validators.MultiFlagsValidator(
        flag_names, multi_flags_checker, message)
    _add_validator(flag_values, v)
docs: Adds a constraint to multiple flags.
  
    The constraint is validated when flags are initially parsed, and after each
    change of the corresponding flag's value.
  
    Args:
      flag_names: [str], a list of the flag names to be checked.
      multi_flags_checker: callable, a function to validate the flag.
          input - dictionary, with keys() being flag_names, and value for each key
              being the value of the corresponding flag (string, boolean, etc).
          output - Boolean. Must return True if validator constraint is satisfied.
              If constraint is not satisfied, it should either return False or
              raise gflags.ValidationError.
      message: Error text to be shown to the user if checker returns False.
          If checker raises gflags.ValidationError, message from the raised error
          will be shown.
      flag_values: An optional FlagValues instance to validate against.
  
    Raises:
      AttributeError: If a flag is not registered as a valid flag name.