public function generate_multi_key_parts() {
        if ($this->keyprefixmulti === null) {
            $this->keyprefixmulti = array(
                'mode' => $this->mode,
                'component' => $this->component,
                'area' => $this->area,
                'siteidentifier' => $this->get_cache_identifier()
            );
            if (isset($this->identifiers) && !empty($this->identifiers)) {
                $identifiers = array();
                foreach ($this->identifiers as $key => $value) {
                    $identifiers[] = htmlentities($key, ENT_QUOTES, 'UTF-8').'='.htmlentities($value, ENT_QUOTES, 'UTF-8');
                }
                $this->keyprefixmulti['identifiers'] = join('&', $identifiers);
            }
        }
        return $this->keyprefixmulti;
    }