- var_dump: documentation ( source)
<?php
$foo = "<p class='description'><a data-ct='campaign_softlayer_inarticle_ad' target='_blank' href='someurl'><img class='lazy-img description' src='someurl' data-original='someurl' /></a></p>";
$dom = new DomDocument();
$dom->loadHtml($foo);
$finder = new DomXPath($dom);
$classname="description";
$nodes = $finder->query("//p[contains(@class, '$classname')]");
var_dump($nodes->length);