public function add_resource_item($module, $title=null, $type, $identifier, $file) {
        $identifier_ref = $identifier."_R";

        $xpath = new \DOMXpath($this);

        $new_item = $this->add_child_ns(CC::CC_1_1_CP, $module, 'item', null, array('identifier' => $identifier, "identifierref" => $identifier_ref));
        if ( $title != null ) {
            $new_title = $this->add_child_ns(CC::CC_1_1_CP, $new_item, 'title', $title);
        }

        $resources = $xpath->query(CC::resource_xpath)->item(0);
        $identifier_ref = $identifier."_R";
        $new_resource = $this->add_child_ns(CC::CC_1_1_CP, $resources, 'resource', null, array('identifier' => $identifier_ref, "type" => $type));
        $new_file = $this->add_child_ns(CC::CC_1_1_CP, $new_resource, 'file', null, array("href" => $file));
        return $file;
    }