PHP 5 permits access to properties and methods of an object that is stored inside in another object. In PHP 4 this required assignment of the object to separate variables.
<?php
class foo {
    public 
$bar 3;
    function 
baz() {
        echo 
$this->bar;
    }
}

class 
bar {
    public 
$o;
    function 
__construct() {
        
$this->= new foo();
    }
}

$a = new bar();
$a->o->baz(); // will print 3
echo $a->o->bar// will also print 3

/* in PHP 4 this would not be possible and require the following kludge */
$tmp =& $a->o;
$tmp->baz();
echo 
$tmp->bar;
?>