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run code in 300+ PHP versions simultaneously
<?php echo "\w without the \u flag should result in int(0) in all PHP versions\n"; var_dump(preg_match('/\w/', 'ä')); echo "\n\w with the \u flag used to result in int(1) in PHP <7.3!\n"; var_dump(preg_match('/\w/u', 'ä')); echo "\n\pL instead of \w used to result in int(1) in all PHP versions\n"; var_dump(preg_match('/\pL/u', 'ä'));

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