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<?php $subject = '1234567890'; preg_replace_callback( '#^([a-z]+)$|^([0-9]+)$#', function ($m) { var_dump($m); return null === $m[1] ? '1' : 'a'; }, $subject, 1, $count, PREG_UNMATCHED_AS_NULL );
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.34, 8.2.0 - 8.2.32, 8.3.0 - 8.3.32, 8.4.1 - 8.4.23, 8.5.0 - 8.5.8
array(3) { [0]=> string(10) "1234567890" [1]=> NULL [2]=> string(10) "1234567890" }

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