final String xpath = xpathConfigMap.get(XPath.DEFAULT_DIGEST);
        if (StringUtil.isNotBlank(xpath)) {
            return xpath;
        }
        return fessConfig.getCrawlerDocumentHtmlDigestXpath();
    }

    /**
     * Extracts the canonical URL from the HTML document.
     *
     * @param responseData the response data from crawling
     * @param document the parsed HTML document

     * comment: XPath to extract digest (description) from HTML documents.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getCrawlerDocumentHtmlDigestXpath();

    /**
     * Get the value for the key 'crawler.document.html.canonical.xpath'. <br>
     * The value is, e.g. //LINK[@rel='canonical'][1]/@href <br>