Quick Primer on XHTML Markup
Writing valid XHTML markup is not really as difficult as it sounds. If you learn a few new rules, you'll be marking up code in valid XHTML in no time. The best way to familiarize yourself with valid markup is to view source on site pages that have passed one of the validation services, such as W3C's Markup Validation Service. Here is a quick rundown of the basics to help you get started.