def METHOD_NAME(self, validation, data):
    """
    Validate this block's field data.
    """
    super().METHOD_NAME(validation, data)
    def add_error(msg):
        validation.add(ValidationMessage(ValidationMessage.ERROR, msg))
    try:
        valid_values = set(self.get_parent().all_choice_values)
    except Exception:
        pass
    else:
        for dummy in set(data.values) - valid_values:
            add_error(self._("A choice selected for this tip does not exist."))