* @param in the input stream to validate
     * @return true if the stream contains valid sitemap data, false otherwise
     */
    public boolean isValid(final InputStream in) {
        return isValid(in, true);
    }

    /**
     * Checks if the given input stream contains valid sitemap data.
     * @param in the input stream to validate

 *
 * <p>
 * The crawling process involves the following steps:
 * </p>
 * <ol>
 *   <li>Fetching a URL from the queue using {@link UrlQueueService#poll(String)}.</li>
 *   <li>Checking if the URL is valid using {@link #isValid(UrlQueue)}.</li>
 *   <li>Accessing the content using a {@link CrawlerClient} obtained from {@link CrawlerClientFactory}.</li>
 *   <li>Processing the response using a {@link ResponseProcessor} associated with a {@link Rule}.</li>

        // Request Header
        final RequestHeader[] requestHeaders = { new RequestHeader("enctype", "multipart/form-data") };
        for (final RequestHeader requestHeader : requestHeaders) {
            if (requestHeader.isValid()) {
                requestHeaderList.add(new BasicHeader(requestHeader.getName(), requestHeader.getValue()));
            }
        }