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run code in 300+ PHP versions simultaneously
<?php $outer=array(); $outer[7]=array('a'=>'aaa','b'=>array()); $inner7=&$outer[7]; $inner7['b'][]='xxx'; $inner7['b'][]='yyy'; print_r($inner7); print_r($outer);

preferences:
37.98 ms | 402 KiB | 5 Q