/** Cache duration in minutes for XPathAPI instances. */
    protected long cacheDuration = 10; // min

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

    /**
     * Initializes the XPathAPI cache with a specified cache duration.
     * This method is called to set up the cache for XPathAPI instances.