QWebPage. How to handle failed request.

Question

I want to handle failed requests (for example, with http 404 error code in reply), display my own "notfound.html" page in QWebView. But there is no simple way to handle replies with QWebView/QWebPage classes.

As I see in Arora browser, for such requests uses next mechanism: QWebPage::setForwardUnsupportedContent(true), QWebPage::unsupportedContent signal and appropriate slot where you can handle qnetworkreply manually. But I cannot understand how it works, because unsupportedContent throws only when QWebPage cannot handle request scheme (like abrakadra://, ftp://, etc) or if reply consists of special header Content-Disposition: attachment.

May be anybody know something about this ?