Why is preg_match case sensitive?

Question

PHP

Hello! I can't understand why even with the i modifier set, preg_match distinguishes between case?

<?php
$text ='монитор Монитор';
$val = strtolower('Монит');

echo preg_replace('/('.$val.'.*?)/i', '<b>$1</b>$2', $text);
?>

Answer 1

Set the modifier u , anything can happen with Cyrillic)
and use mb_* when dealing with Cyrillic, so that there are fewer surprises