What is it?
XHTML (Extensible Hypertext Markup Language) is a markup language for web pages that combines HTML with XML. It was intended to replace HTML, but there is no sign of this happening on a wide scale yet.
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Even so, the World Wide Web Consortium (W3C) is set to approve XHTML2 next year. This could create an even bigger step, and a greater range of backward compatibility problems for those who have ignored XHTML.
It would not be the first time that users have frustrated the plans of the technocrats by sticking with a popular technology.
But in the case of XHTML, the arguments to switch seem strong, even if they are often couched in terms that appeal only to a dedicated minority.
Standardisation means greater device independence, and could eliminate much of the time wasted checking browser compatibility. Standardised web pages can be understood by XML-savvy applications, as well as by people.
XHTML has been described as offering "all the benefits of XML while avoiding the complications of true XML" - bridging the gap for HTML developers who might not fancy taking on something as tricky as full XML.
Where did it originate?
In 1999, the W3C brought out HTML 4.0 and XHTML, which was essentially HTML 4.0 recast into XML. The W3C said XHTML brought "the rigour of XML to HTML".
HTML, XML and XHTML all derive from SGML (Standard Generalised Markup Language). XHTML2 is intended to represent "a complete break from the non-XML heritage of HTML".
What is it for?
According to Steven Pemberton, chair of the HTML and forms working groups at the W3C, the design aims of XHTML 2.0 include using XML as much as possible.
He said, "Where a language feature already exists in XML, do not duplicate or reinvent it." The emphasis is on structure over presentation.
"Thanks to Cascading Stylesheets (CSS), you no longer need explicitly presentational tags in HTML." And by removing some of the "needless idiosyncracies" of HTML, it should make it easier to maintain, if not to write.
What makes it special?
Apart from the advantages of standardisation, greater interoperability will be possible between XHTML and other XML languages. Semantic web applications will be able to use XHTML documents.
How difficult is it to master?
HTML developers are said to be able to pick up XHTML in their spare time in about a week.
What is coming up?
XHTML2 is not likely to become a W3C recommendation until 2007. In the meantime, acquiring the skills could give you the edge in a vibrant new jobs market - bearing in mind there may be no immediate upsurge of XHTML2 work.
According to IBM's Developerworks site, you can prepare by getting serious about using CSS and removing presentational mark-up.
Rates of pay
XHTML developers can earn £30,000, rising to £35,000 with more experience.
You can pay for XHTML training, but there are thousands of free tutorials. For a proper understanding, start with the W3C site or look for books by the W3C's HTML/XHTML expert Dave Raggett.
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