3v4l.org

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<?php for ($i = 0; $i < 0x10ffff; $i++) { $chr = mb_chr($i); if (strlen($chr) !== strlen(mb_strtolower($chr)) || strlen($chr) !== strlen(mb_strtoupper($chr))) { var_dump($i); var_dump($chr); var_dump(mb_strtolower($chr)); var_dump(mb_strtoupper($chr)); break; } }
Output for 7.4.0 - 7.4.33, 8.0.1 - 8.0.30, 8.1.0 - 8.1.33, 8.2.0 - 8.2.29, 8.3.0 - 8.3.27, 8.4.1 - 8.4.14
int(304) string(2) "İ" string(3) "i̇" string(2) "İ"

preferences:
135.7 ms | 406 KiB | 5 Q