*  @param expression A valid XPath string.
     *  @return A XPathNodes, should never be null.
     *
     * @throws XPathExpressionException if an XPath expression error occurs.
     */
    public XPathNodes selectNodeList(final Node contextNode, final String expression) throws XPathExpressionException {
        return xPath.evaluateExpression(expression, contextNode, XPathNodes.class);
    }

    /**

        }
    }

    /**
     * Adds a client with a regular expression pattern.
     * @param regex The regular expression to match URLs.
     * @param client The CrawlerClient instance.
     */
    public void addClient(final String regex, final CrawlerClient client) {
        if (StringUtil.isBlank(regex)) {
            throw new CrawlerSystemException("A regular expression is null.");
        }
        if (client == null) {

     */
    public PasswordBasedExtractor() {
        super();
    }

    /**
     * Adds a password for files matching the given regular expression pattern.
     * @param regex the regular expression pattern to match against URLs or resource names
     * @param password the password to use for matching files
     */
    public void addPassword(final String regex, final String password) {

    boolean match(String url);

    /**
     * Add an url pattern as a target.
     *
     * @param urlPattern Regular expression that is crawled
     */
    void addInclude(String urlPattern);

    /**
     * Add an url pattern as a non-target.
     *
     * @param urlPattern Regular expression that is not crawled
     */
    void addExclude(String urlPattern);

    /**

     * @return a list of compiled regular expression patterns representing the URLs to include
     */
    List<Pattern> getIncludeUrlPatternList(String sessionId);

    /**
     * Retrieves a list of URL patterns to be excluded for a given session.
     *
     * @param sessionId the identifier of the session for which to retrieve the exclude URL patterns
     * @return a list of compiled regular expression patterns representing the URLs to be excluded

    }

    /**
     * Adds a regular expression rule for the specified field.
     * @param key the field name to match against
     * @param regex the regular expression pattern
     */
    public void addRule(final String key, final String regex) {
        regexMap.put(key, Pattern.compile(regex));
    }

    /**
     * Adds a compiled regular expression rule for the specified field.

            clientFactoryList.remove(0);
        }
    }

    /**
     * Registers a client component with a regular expression.
     * The component will be loaded into all registered CrawlerClientFactories.
     * @param regex The regular expression to match URLs.
     * @param componentName The name of the component to register.
     */

 * It uses XPath expressions to extract text content from HTML documents.
 * <p>
 * This class provides methods to configure the XPath expressions, parser features, and properties.
 * It also includes caching mechanism for XPathAPI instances to improve performance.
 * </p>
 * <p>
 * The extracted text is obtained from the nodes selected by the {@code targetNodePath} XPath expression.

        } finally {
            xpathAPI.remove();
        }
    }

    /**
     * Extracts strings from a document using the specified XPath expression.
     *
     * @param document the DOM document to extract strings from
     * @param path the XPath expression to evaluate
     * @return an array of strings extracted from the document
     */

    @Override
    public void close() {
        clientFactory.close();
    }

    /**
     * Adds an include filter for URLs.
     * Only URLs matching this regular expression will be crawled.
     * @param regexp The regular expression for the include filter.
     */
    public void addIncludeFilter(final String regexp) {
        if (StringUtil.isNotBlank(regexp)) {
            urlFilter.addInclude(regexp);
        }