如何判断UIWebView中iframe加载与整个页面加载的区别？

In the [webView:shouldStartLoadWithRequest:navigationType:] event, how can you tell the difference between an iframe that's loading content vs. the entire page loading content? It seems like the both call this same event with the same arguments, the only difference being the URL that's going to be loaded, so there is no way to tell the difference between the two.In the [webView:shouldStartLoadWithRequest:navi