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<?php var_dump(preg_match('/^\b([a-z0-9] ?)+$\b/i', 'this works'), preg_match('/^\b([a-z0-9] ?)+$\b/i', 'this should not work'));
Output for 5.5.0 - 5.5.35, 5.6.0 - 5.6.28, 7.0.0 - 7.0.20, 7.1.0 - 7.1.20, 7.2.0 - 7.2.33, 7.3.16 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
int(1) int(0)
preferences:
208.46 ms | 404 KiB | 213 Q