protected function processMetaTags(array &$tags)
    {
        // Call hook
        GeneralUtility::callHookAndSignal(__CLASS__, 'metatagOutput', $this, $tags);

        // Add marker
        $markerList = array(
            '%YEAR%' => date('Y'),
        );

        $keyList = array(
            'meta.title',
            'meta.description',
            'meta.description.dc',
            'meta.keywords',
            'meta.keywords.dc',
            'meta.copyright',
            'meta.copyright.dc',
            'meta.publisher.dc',
        );

        foreach ($keyList as $key) {
            if (!empty($tags[$key]['attributes'])) {
                foreach ($markerList as $marker => $value) {
                    foreach ($tags[$key]['attributes'] as &$metaTagAttribute) {
                        // only replace markers if they are present
                        if (strpos($metaTagAttribute, $marker) !== false) {
                            $metaTagAttribute = str_replace($marker, $value, $metaTagAttribute);
                        }
                    }
                    unset($metaTagAttribute);
                }
            }
        }
    }