protected void AppendHTMLToWebBrowser(WebBrowser browser, IPrintableHTML htmlItem)
 {
     if (InvokeRequired) {
         AppendHTMLToWebBrowserCallback c = AppendHTMLToWebBrowser;
         Invoke(c, new object[] { browser, htmlItem });
     } else {
         browserBody.Append(htmlItem.ToHTML());
         browser.DocumentText = browserHeader + browserBody + browserFooter;
     }
 }