protected function extractContentMarkedForIndexing($html)
    {
        preg_match_all('/<!--\s*?TYPO3SEARCH_begin\s*?-->.*?<!--\s*?TYPO3SEARCH_end\s*?-->/mis',
            $html, $indexableContents);
        $indexableContent = implode($indexableContents[0], '');

        $indexableContent = $this->excludeContentByClass($indexableContent);
        if (empty($indexableContent) && $this->getConfiguration()->getLoggingIndexingMissingTypo3SearchMarkers()) {
            $this->logger = GeneralUtility::makeInstance(SolrLogManager::class, /** @scrutinizer ignore-type */ __CLASS__);
            $this->logger->log(SolrLogManager::WARNING, 'No TYPO3SEARCH markers found.');
        }

        return $indexableContent;
    }