Changes in reference handling
Integer values in function parameters
Migrating from PHP 5.0.x to PHP 5.1.x
PHP Manual

## Reading []

`<?php
class XmlTest {
function test_ref(&$test) {
$test = "ok";
}
function test($test) { }
function run() {
$ar = array();
$this->test_ref($ar[]);
var_dump($ar);
$this->test($ar[]);
}
}
$o = new XmlTest();
$o->run();
?>`

This should always have thrown a fatal `E_ERROR`, because [] cannot be used for reading in PHP. It is invalid code in PHP 4.4.2 and PHP 5.0.5 upward.