php 多维数组取得键值的疑问？

Question

eg: 
$arr = array(
    'A' => array(
        'A1' => 'first A',
        'A2' => array(
            'A2A' => 'second A')
    )
)

如何返回某个值的所有维度的键值？返回值'secend A'的每层键值'A2A', 'A2' , 'A' ?

Answer 1

Questions about obtaining key values ​​from multi-dimensional arrays in php? -PHP Chinese website Q&A-Questions about obtaining key values ​​from multi-dimensional arrays in PHP? -PHP Chinese website Q&A

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Answer 2

不知道在说什么。。。。