Beware of XHTML

"If you're a web developer, you've probably heard about XHTML, the markup language developed in 1999 to implement HTML as an XML format. Most people who use and promote XHTML do so because they think it's the newest and hottest thing, and they may have heard of some (usually false) benefits here and there. But there is a lot more to it than you may realize, and if you're using it on your website, even if it validates, you are probably using it incorrectly. I should make it clear that I hope XHTML has a bright future on the Web."