[]= could be considered an Array Operator (in the same way that .= is a String Operator).
[]= pushes an element onto the end of an array, similar to array_push:
<?
$array= array(0=>"Amir",1=>"needs");
$array[]= "job";
print_r($array);
?>
Prints: Array ( [0] => Amir [1] => needs [2] => job )