/** Map of metadata field names to their corresponding XPath expressions. */
    protected Map<String, String> metadataXpathMap = new HashMap<>();

    /** Thread-local instance of XPathAPI for thread-safe XPath evaluation. */
    private final ThreadLocal<XPathAPI> xpathAPI = new ThreadLocal<>();

    /**
     * Creates a new HtmlExtractor instance.
     */
    public HtmlExtractor() {
        super();
    }

import org.codelibs.fess.crawler.exception.CrawlerSystemException;
import org.w3c.dom.Node;

/**
 * The XPathAPI class provides methods to evaluate XPath expressions and select nodes or node lists from an XML document.
 * It uses the javax.xml.xpath.XPath and javax.xml.xpath.XPathFactory classes to create and evaluate XPath expressions.
 *
 * <p>Example usage:</p>
 * <pre>
 * {@code
 * XPathAPI xPathAPI = new XPathAPI();

 * <p>
 * This class extends {@link HtmlTransformer} and overrides the {@link #storeData(ResponseData, ResultData)} method
 * to parse the HTML content, evaluate XPath expressions, and generate the XML output.
 * </p>
 * <p>
 * The class supports various XPath result types, including BOOLEAN, NUMBER, STRING, NODESET, and NODE.