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<?php $age=array("Peter"=>"35","Ben"=>"37","Joe"=>"43", 'Blow' => array('Job'=>666)); print_r(array_change_key_case($age,CASE_LOWER)); ?>
Output for 4.3.0 - 7.1.0
Array ( [peter] => 35 [ben] => 37 [joe] => 43 [blow] => Array ( [Job] => 666 ) )