使用xpath获取节点值不返回值

Question

我正在使用xpath获取某些节点的值。以下是示例xml：

<Order>
<OrderNumber>2112491630</OrderNumber>
<OrderId>9876543</OrderId>
<OrderDetails>
    <OrderDetail>
        <SKUData>
            <SKUQuestions>
                <SKUQuestion>
                    <Tag>PowerOn</Tag>
                    <Question>Does the Device Power On?</Question>
                    <Answer>Yes</Answer>
                </SKUQuestion>
                <SKUQuestion>
                    <Tag>OtherIssues</Tag>
                    <Question>Please describe the issue(s) the device is experiencing in detail</Question>
                    <Answer>Im a pineapple</Answer>
                </SKUQuestion>
            </SKUQuestions>
        </SKUData>
    </OrderDetail>
    <OrderDetail>
        <SKUData>
            <SKUQuestions>
                <SKUQuestion>
                    <Tag>PowerOn</Tag>
                    <Question>Does the Device Power On?</Question>
                    <Answer>Yes</Answer>
                </SKUQuestion>
                <SKUQuestion>
                    <Tag>OtherIssues</Tag>
                    <Question>Please describe the issue(s) the device is experiencing in detail</Question>
                    <Answer>Im a banana</Answer>
                </SKUQuestion>
            </SKUQuestions>
        </SKUData>
    </OrderDetail>
</OrderDetails>

这是php：

<?php

foreach($files as $filename) {

    $xml=simplexml_load_file($filename) or die("Error: Cannot create object");

    foreach($xml->OrderDetails->OrderDetail as $orderDetail) {

        $qOtherIssues = $orderDetail->xpath('/SKUData/SKUQuestions/SKUQuestion[Tag="OtherIssues"]');
    foreach($qOtherIssues as $a) {
        $otherIssues = str_replace("'", "\'", $a->Answer);
        }

    $qPowerOn = $orderDetail->xpath('/SKUData/SKUQuestions/SKUQuestion[Tag="PowerOn"]');
    foreach($qPowerOn as $a) {
        $powerOn = str_replace("'", "\'", $a->Answer);
        }

    }
}

}     ？＆GT;

使用绝对xpath设置，它不会为问题组返回任何内容。

当我使用通配符（//）作为路径时，它只返回最后一组问题（我是香蕉等）。我想在每个OrderDetail标记中返回一组问题。

我迷路了。