What types of files can the built in iPad Web Browser handle natively?

What types of files can the built in iPad UIWebView handle natively? It seems to handle PDF files and image files fine with loadRequest URL's, but it can't handle Excel spreadsheets. What开发者_如何转开发 is the complete list of files that it is capable of showing natively?

Apple's documentation is here:

http://developer.apple.com/iphone/library/qa/qa2008/qa1630.html#//apple_ref/doc/uid/DTS40008749

They claim it does support Excel (.xls); perhaps you have a xlsx or a problem with mimetypes on the server? (Though that list is the iPhone OS 3.0 list, but I can't see why they'd have removed any supported formats on the iPad.)