奇怪的json_decode有关问题，为什么不能decode呢

奇怪的json_decode问题，，为什么不能decode呢？

PHP code

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<?php $rm = '5e
?{"return":"error","errorcode":400,"errorinfo":"\u7528\u6237\u540d\u5df2\u88ab\u6ce8\u518c"}
0'; //注意这里面有2个换行符，在5e后面和0前面
    $a_rm = explode("\r\n", $rm);
    $a_rm1 = $a_rm[1];
    echo $a_rm1;
    echo "<pre class="brush:php;toolbar:false">";var_dump(json_decode($a_rm1, true));
?>

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PHP code

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-->{"return":"error","errorcode":400,"errorinfo":"\u7528\u6237\u540d\u5df2\u88ab\u6ce8\u518c"}

NULL

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PHP code

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$aa = '{"return":"error","errorcode":400,"errorinfo":"\u7528\u6237\u540d\u5df2\u88ab\u6ce8\u518c"}';
    var_dump(json_decode($aa))

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