As we’ve seen in other articles in this series, XHTML offers a lot of advantages over HTML. It’s stricter, cleaner, more robust, and extensible. However, some modern browsers such as Internet Explorer don’t understand XHTML; they only understand HTML 4. Fortunately, the two languages are very similar and, by bearing a few guidelines in mind, you can write valid XHTML documents that can be processed correctly by HTML 4 browsers.