What is it?
XHTML is intended to replace HTML (Hypertext Markup Language), bringing the "rigour of XML" to it.
XHTML is also a bridge to making HTML a full subset of XML.
Where did it originate?
HTML was devised by Tim Berners-Lee, creator of the Web. It is based on SGML (Standard Generalised Markup Language) but is much simpler. While HTML's easy-going nature made it the Web's lingua franca, it also led to sloppy coding. XML, also an offspring of SGML, keeps the richness of the language while making it simpler to use. XML coding is much more disciplined. For example, all elements must have closing tags.
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The World-Wide Web Consortium (W3C) working group on XHTML included people from Sun, IBM, HP, Microsoft, Quark and AskJeeves.
What is it for?
XHTML will work with browsers like Internet Explorer and Netscape Navigator, and is backward-compatible with HTML. Existing HTML pages can be reused in sites that adopt XHTML, using W3C's open source HTML Tidy utility. XHTML documents can be viewed, edited, and validated with standard XML tools.
What makes it special?
Benefits promised by W3C include reduced authoring costs, an improved match for database and workflow applications, and the ability to integrate HTML with other XML applications. XML applications are more efficient to process and easier to maintain.
What does it run on?
All Web platforms. In addition to XHTML 1.90, there is XHTML Basic, a core subset for use on small-memory, low-power and low-bandwidth platforms such as PDAs and mobile phones. "The modular design of XHTML reflects the realisation that a one-size-fits-all approach will no longer work in a world where browsers vary enormously in their capabilities," the W3C explains.
How difficult is it?
The W3C recommends that beginners learn XHTML rather than HTML. It says experienced HTML authors will find the learning curve short.
Where is it used?
XHTML will eventually replace HTML - although, with literally billions of HTML pages currently in use, the transition is likely to take a long time.
XHTML developers with ex-HTML developers.
What's coming up?
Being modular, XHTML can be extended as platforms develop - adding scripting to the handheld version, for example.
You can take paid-for HTML courses with most major training companies, but there is plenty of free material on the Internet. The best place to start is the W3C Web site (www.W3.org), where W3C HTML guru Dave Raggett has posted tutorials for HTML, advanced HTML, XHTML and Tidy.
You can teach yourself XHTML with a text editor and a book. Raggett on HTML 4 is published by Addison-Wesley. Raggett is also co-author of XHTML Example by Example, to be published by Prentice Hall/Sun Microsystems in March. Another good source is Beginning XHTML, published last year by Wrox Press.
Rates of pay
Rates for HTML have dropped over the last year because it has become a commodity skill and because some Web development tools can generate HTML code. Even with XHTML, Web interface designers are offered as low as £12,000 to £15,000 in London. It is what you bring with it that counts, and the best rates are for skills such as Broadvision and Coldfusion.