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.

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