<?php

function test() {
    var_dump($GLOBALS['x']);
    $GLOBALS['x'] = 1;
    var_dump($GLOBALS['x']);
    $GLOBALS['x']++;
    var_dump($GLOBALS['x']);
    $GLOBALS['x'] += 2;
    var_dump($GLOBALS['x']);
    unset($GLOBALS['y']);
    var_dump(isset($GLOBALS['x']));
    var_dump(isset($GLOBALS['y']));
    $GLOBALS['z'][] = 1;
}

$y = 1;
test();
var_dump($x, $y, $z);

$ref = 1;
$GLOBALS['z'] =& $ref;
$ref++;
var_dump($z);

$x = 1;
$ref2 =& $GLOBALS['x'];
$ref2++;
var_dump($x);

?>