DOMXpath并获得结果

I try to get the result of a span tag like this:

The problem, the span class is often names css "AB" into the html code and I want to get the one span tag with the itemprop ratingvalue, only.

<span class="AB" itemprop='ratingValue'>Count</span>

In php I use generally this code:

   $html= file_get_contents('url');

$html = escapeshellarg($html);
        $html = nl2br($html);

    $dom = new DOMDocument;
        $dom->loadHTML($html);
        $xpath = new DOMXPath($dom);
        $results = $xpath->query("//*[@itemprop='ratingValue']");

        if ($results->length > 0) {
            echo $review_count_html = $results->item(0)->nodeValue;
        }

This code does run generally, but by this request I get no results. Can anybody help me? Thanks a lot.

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