<ul class="c1 c2 c3">
    <li class="c11 c12" attrib-1 ... attrib-n>
        //More tags
        <span a="vx">
            <span b="name1">txt1</span>
            <span b="name2">txt2</span>
            //more <span>
        </span>
        <span a="vy">
            <span b="name3">txt3</span>
            <span b="name4">txt4</span>
            //more <span>
        </span>
        //More tags
    </li>
    //Many more <li>

$xpath = new DOMXPath($doc);
$e = $xpath->query("//div[@id='_1']//ul[contains(@class, 'c2')]//descendant-or-self::li[contains(@class, 'c11') and @attrib-1]");

foreach($e as $li) {
    $z = $xpath->query(".//descendant::span[contains(@a,'v')]",$li);
    //Changed this section a lot. Loop / no-loop / various degrees of trying to access first Node in nodeList, etc
    var_dump(/*some var*/);//die();
}