A Guide to HTML5 Features You Can’t Detect
Web developers looking to play with the new features in HTML5, CSS 3 and other NEWT tools are still struggling with incomplete and inconsistent browser support. While HTML5 and its siblings are far from perfect (and complete), that doesn’t mean you can’t use them; it just means using them is a little more complicated since you need to detect the current browser’s level of support and then adjust accordingly.
The page lists a number of features that simply can’t be detected using general feature tests. Instead, these features can be found by either user agent sniffing (which leads to heartache and doom), browser inferences or as the wiki puts it “simply providing the same (slow) fix to everyone.”
If your code has been behaving strangely, despite your best efforts to detect a browser’s features, save yourself some hair pulling and head over the new Modernizr page to see if perhaps the problem is on the list of things that can’t be detected. If you discover other problems trying to sniff a browser’s capabilities, be sure to let the Modernizr devs know about it.