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run code in 200+ php & hhvm versions
<?php var_dump(mb_regex_set_options("m")); var_dump(mb_regex_set_options("mdi")); var_dump(mb_regex_set_options("m")); var_dump(mb_regex_set_options("a"));
Output for 5.6.38 - 7.2.11
string(2) "mr" string(3) "imd" string(2) "mr" string(1) "r"