echo (new \DateInterval('P3W2D'))->format('%d');
// outputs '2' prior PHP 8.0
// outputs '23' in PHP >= 8.0

        if (!$this->isISO8601($data)) {
            throw new UnexpectedValueException('Expected a valid ISO 8601 interval string.');
        }

// PHP >= 8.0
$normalizer = new \Symfony\Component\Serializer\Normalizer\DateIntervalNormalizer();
$object = $normalizer->denormalize('P2W6D', \DateInterval::class, null, [
    'dateinterval_format' => '%rP%yY%mM%wW%dDT%hH%iM%sS',
]);
// expected: $object instanceof \DateInterval
// actual: \Symfony\Component\Serializer\Exception\UnexpectedValueException thrown

    private function isISO8601(string $string): bool
    {
        if (PHP_VERSION_ID >= 80000) {
            return preg_match('/^[\-+]?P(?=\w*(?:\d|%\w))(?:\d+Y|%[yY]Y)?(?:\d+M|%[mM]M)?(?:\d+W|%[wW]W)?(?:\d+D|%[dD]D)?(?:T(?:\d+H|[hH]H)?(?:\d+M|[iI]M)?(?:\d+S|[sS]S)?)?$/', $string);
        }

        return preg_match('/^[\-+]?P(?=\w*(?:\d|%\w))(?:\d+Y|%[yY]Y)?(?:\d+M|%[mM]M)?(?:(?:\d+D|%[dD]D)|(?:\d+W|%[wW]W))?(?:T(?:\d+H|[hH]H)?(?:\d+M|[iI]M)?(?:\d+S|[sS]S)?)?$/', $string);
    }