array_search 1. :
<?php
$array = array(0 => 'blue', 1 => 'red', 2 => 'green', 3 => 'red');
$key = array_search('blue', $array);
?>
, , 0.
, == === . array_search 0, , :
if (false == array_search(...)) { ... }
===, ,
// works, even when element 0 is matched
if (false === array_search(...)) { ... }