public function rels(array $urns)
    {
        $rawLinks = [];
        foreach ($this as $i => $link) {
            if (!empty($link->rels)) {
                $match = array_diff($urns, $link->rels);
                if (count($match) != count($urns)) {
                    $rawLinks[] = $this->_links[$i];
                }
            }
        }
        return new CollectionDocJsonLinks($rawLinks, $this->_auth);
    }