protected function validateBreak(Break_ $break)
    {
        $strength = $break->strength;
        if ($strength !== null && !in_array($strength, self::BREAK_STRENGTHS, true)) {
            throw new InvalidAttributeValueException(
                $break, 'strength', $strength, self::BREAK_STRENGTHS, 'alexa'
            );
        }

        $time = $break->time;
        if ($time !== null && preg_match('/^\d+m*s+$/', $time) === 0) {
            throw new InvalidAttributeValueException(
                $break, 'time', $time, '\d[m*s+]', 'alexa'
            );
        }
    }