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run code in 200+ php & hhvm versions
<?php mb_ereg('(?<word>\w+)', '国', $matches); print_r($matches);
based on UPHF6
Output for 7.3.0
Array ( [0] => 国 [1] => 国 [word] => 国 )
Output for 5.6.38 - 7.2.13
Array ( [0] => 国 [1] => 国 )