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<?php $str = "it is a test string."; echo preg_replace(['~\Ar~', '~.{3}\K(?>r|.(*SKIP)(?!))~'], 'm', $str);
Output for 7.0.0 - 7.0.25, 7.1.0 - 7.1.33, 7.2.6 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.31, 8.2.0 - 8.2.26, 8.3.0 - 8.3.15, 8.4.1 - 8.4.2
it is a test stming.
preferences:
94.48 ms | 407 KiB | 5 Q