The union operator did not behave as I thought it would on first glance. It implements a union (of sorts) based on the keys of the array, not on the values.For instance:<?php$a = array('one','two');$b=array('three','four','five');//not a union of arrays' valuesecho '$a + $b : ';print_r ($a + $b);//a union of arrays' valuesecho "array_unique(array_merge($a,$b)):";// cribbed from http://oreilly.com/catalog/progphp/chapter/ch05.htmlprint_r (array_unique(array_merge($a,$b)));?>//output$a + $b : Array(    [0] => one    [1] => two    [2] => five)array_unique(array_merge(Array,Array)):Array(    [0] => one    [1] => two    [2] => three    [3] => four    [4] => five)

The example may get u into thinking that the identical operator returns true because the key of apple is a string but that is not the case, cause if a string array key is the standart representation of a integer it's gets a numeral key automaticly. The identical operator just requires that the keys are in the same order in both arrays:<?php$a = array (0 => "apple", 1 => "banana");$b = array (1 => "banana", 0 => "apple");var_dump($a === $b); // prints bool(false) as well$b = array ("0" => "apple", "1" => "banana");var_dump($a === $b); // prints bool(true)?>

Note that + will not renumber numeric array keys.  If you have two numeric arrays, and their indices overlap, + will use the first array's values for each numeric key, adding the 2nd array's values only where the first doesn't already have a value for that index.  Example:$a = array('red', 'orange');$b = array('yellow', 'green', 'blue');$both = $a + $b;var_dump($both);Produces the output:array(3) { [0]=>  string(3) "red" [1]=>  string(6) "orange" [2]=>  string(4) "blue" }To get a 5-element array, use array_merge.    Dan

$a=[ 3, 2, 1];$b=[ 6, 5, 4];var_dump( $a + $b );output:array(3) {  [0]=>  int(3)  [1]=>  int(2)  [2]=>  int(1)}The reason for the above output is that EVERY array in PHP is an associative one.  Since the 3 elements in $b have the same keys( or numeric indices ) as those in $a, those elements in $b are ignored by the union operator.

[]= 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 )

It should be mentioned that the array union operator functions almost identically to array_replace with the exception that precedence of arguments is reversed.

Merge two arrays and retain only unique values.Append values from second array.Do not care about keys.<?php$array1 = [    0 => 'apple',    1 => 'orange',    2 => 'pear',];$array2 = [    0 => 'melon',    1 => 'orange',    2 => 'banana',];$result = array_keys(    array_flip($array1) + array_flip($array2));?>Result:[  [0] => "apple",  [1] => "orange",  [2] => "pear",  [3] => "melon",  [4] => "banana",}