关于PHP手册中，不推荐复杂数组的引用举的一个例子，不解

Question

下面是手册里的原文：复杂数组最好拷贝而不是引用。下面的例子不会如期望中那样工作。<?php
$top = array(
    'A' => array(),
    'B' => array(
        'B_b' => array(),
    ),
);$top['A']['parent'] = &$top;
$top['B']['parent'] = &$top;
$top['B']['B_b']['data'] = 'test';
print_r($top['A']['parent']['B']['B_b']); // array()
?> 
我输出的结果为：Array ( [data] => test ) ，这不就是预期的吗？
$top['A']['parent']为$top变量的引用，（$top['A']['parent'] = &$top;）
它下边的['B']['B_b']，
不就是由$top['B']['B_b']['data'] = 'test';定义的[data] => test吗？
怎么会不如预期那样工作呢？预期怎么样工作呢？

Answer 1

手册哪里？ 
没找到这段啊这里是用的另外一个例子
http://www.php.net/manual/zh/language.references.arent.php

Answer 2

输出一下每步的结构就可以看得比较清楚：
$top = array(
            'A' => array(),
            'B' => array(
                'B_b' => array(),
            ),
        );        $top['A']['parent'] = &$top;
        echo '<pre>';
        print_r($top['A']['parent']);
        echo '</pre>';
        echo '<pre>';
        $top['B']['parent'] = &$top;
        echo '</pre>';
        echo '<pre>';
        print_r($top['B']['parent']);
        echo '</pre>';
        echo '<pre>';
        $top['B']['B_b']['data'] = 'test';
        print_r($top['B']['B_b']);
        echo '</pre>';
        echo '<pre>';
        print_r($top['A']['parent']['B']['B_b']); // array()
        echo '</pre>';
        echo '<pre>';
运行结果如下：
Array
(
    [A] => Array
        (
            [parent] => Array
                (
                    [A] => Array
 *RECURSION*
                    [B] => Array
                        (
                            [B_b] => Array
                                (
                                )                        )                )        )    [B] => Array
        (
            [B_b] => Array
                (
                )        ))
Array
(
    [A] => Array
        (
            [parent] => Array
                (
                    [A] => Array
 *RECURSION*
                    [B] => Array
                        (
                            [B_b] => Array
                                (
                                )                            [parent] => Array
 *RECURSION*
                        )                )        )    [B] => Array
        (
            [B_b] => Array
                (
                )            [parent] => Array
                (
                    [A] => Array
                        (
                            [parent] => Array
 *RECURSION*
                        )                    [B] => Array
 *RECURSION*
                )        ))Array
(
    [data] => test
)Array
(
    [data] => test
)
$top['A']['parent']['B']['B_b']的结果为：
Array
(
    [data] => test
)