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run code in 200+ php & hhvm versions
<?php $utf8='η.∊'; var_dump($utf8, mb_convert_encoding($utf8,'CP1252','UTF-8'), mb_convert_encoding(mb_convert_encoding($utf8,'CP1252','UTF-8'),'UTF-8','CP1252') );
based on gIpst
Output for 7.1.25 - 7.3.2
string(6) "η.∊" string(3) "?.?" string(3) "?.?"