Description:
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When trying to get all elements from the default namespace (by providing an empty string first argument) getElementsByTagNameNS returns elements from ALL namespaces.

In the provided example, getElementsByTagNameNS should return only the first "a" element, not both.

Test script:
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$doc = new DOMDocument();
$doc->loadXML('<root xmlns:x="x"><a/><x:a/></root>');
$list = $doc->getElementsByTagNameNS('', 'a');
echo $list->length;


Expected result:
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1

Actual result:
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2