So What's a Web Application Developer To Do in This New World?
XSLT can be used to transform XML content to device-specific formats. By detecting the user agent string, you can adapt your content through a specific style sheet to that user agent. The user agent contains both, but do you really want to have a different XSLT style sheet sitting around for every device you want to address, for each kind of content? That could easily add up to thousands of XSLT style sheets just for one application. The reality is that, for most applications, you don't need to consider every user agent.