def handle_format_group(self, field, text):
        """Handle format group."""

        # Handle auto incrementing group indexes
        if field == '':
            if self.auto:
                field = str(self.auto_index)
                text[0] = (_util.FMT_FIELD, field)
                self.auto_index += 1
            elif not self.manual and not self.auto:
                self.auto = True
                field = str(self.auto_index)
                text[0] = (_util.FMT_FIELD, field)
                self.auto_index += 1
            else:
                raise ValueError("Cannot switch to auto format during manual format!")
        elif not self.manual and not self.auto:
            self.manual = True
        elif not self.manual:
            raise ValueError("Cannot switch to manual format during auto format!")

        self.handle_group(field, tuple(text), True)
Handle format group.