QueryPath\DOMQuery::addClass PHP Method

    public function addClass($class)
    {
        foreach ($this->matches as $m) {
            if ($m->hasAttribute('class')) {
                $val = $m->getAttribute('class');
                $m->setAttribute('class', $val . ' ' . $class);
            } else {
                $m->setAttribute('class', $class);
            }
        }
        return $this;
    }