The only array operator in PHP is the + operator. It appends the right handed array to the left handed, whereas duplicated keys are NOT overwritten.
<?php$a = array("a" => "apple", "b" => "banana");$b = array("a" =>"pear", "b" => "strawberry", "c" => "cherry");$c = $a + $b;var_dump($c);?>
array(3) { ["a"]=> string(5) "apple" ["b"]=> string(6) "banana" ["c"]=> string(6) "cherry"}
See also the manual sections on the Array type and Array functions.