Extensible Hypertext Markup Language
This article takes a pragmatic look at XHTML, a markup language that effectively bridges the gap between the simplicity of HTML and the extensibility of XML. It also covers the essential features of the various flavors of XHTML and includes discussions of the language and a number of real-world applications.
Being a Web developer is a tough job. Not only do you have to steer clear of the traps and pitfalls that the popular browsers throw at you on a daily basis, but you also have to keep at least half an eye on the myriad developments that may (or may not) have an impact on your job. You may have just barely mastered style sheets and DHTML, yet new techniques clamor for your attention. Which ones do you need to learn right away? Which ones can you dismiss for now? Traditional HTML may ultimately be put out to pasture with the emergence of Extensible Hypertext Markup Language, or XHTML.
XHTML is a hybrid of HTML and XML that's specifically designed for Net device displays (which include Web browsers, PDA devices, and cell phones). January 26, 2002 marked the second birthday of XHTML 1.0 as the official W3C recommendation for Web markup. But XHTML has yet to toddle, yet to smile, and yet to cry loud enough to get the attention of most Web designers.
W3C director Tim Berners-Lee put it this way: "XHTML 1.0 connects the present Web to the future Web...It provides the bridge to page and site authors for entering the structured data, XML world, while still being able to maintain operability with user agents that support HTML 4."
XHTML is a fairly rigid markup language. Its rules are very straightforward, and it really has very little extensibility -- that is, you can't write your own definitions to dictate how the language behaves; you've got to follow its rules. XHTML 1.0 adopts concepts that were introduced in HTML 4.0, which requires structured and methodological behavior before it is valid.
XHTML can be used with cascading style sheets (CSS) to achieve presentation goals. XHTML also allows you to use Extensible Stylesheet Language (XSL) with transformations. By using this XML-based style technology, you can actually transform a document from one type to another -- say, from an HTML document to a PDF document.