关于PHP手册中，不推荐复杂数组的引用举的一个例子，不解,该怎么处理

 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()
?> 

$top = array(
            'A' => array(),
            'B' => array(
                'B_b' => array(),
            ),
        );

        $top['A']['parent'] = &$top;
        echo '
';
        print_r($top['A']['parent']);
        echo '
';
        echo '
';
        $top['B']['parent'] = &$top;
        echo '
';
        echo '
';
        print_r($top['B']['parent']);
        echo '
';
        echo '
';
        $top['B']['B_b']['data'] = 'test';
        print_r($top['B']['B_b']);
        echo '
';
        echo '
';
        print_r($top['A']['parent']['B']['B_b']); // array()
        echo '
';
        echo '
';