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run code in 300+ PHP versions simultaneously
<?php $str = "Hello, this is a test"; $str = preg_replace_callback('/(\w*)(\w)/u', function($m) { return mb_strtoupper($m[1]).mb_strtolower($m[2]); }, $str); echo $str;

preferences:
31.46 ms | 406 KiB | 5 Q