In the SSL/CW list of top IT skills, HTML is number 15.
What is it?
The World Wide Web Consortium (W3C) described HTML (Hypertext Markup Language) as "the lingua franca for publishing on the world wide web". It is universal, easy to use and very stable - the latest revision, HTML 4.01, was published in December 1999.
Also in 1999, the W3C brought out Extensible HTML (XHTML), which was essentially HTML 4.0 recast into XML. The W3C said XHTML brought "the rigour of XML to HTML". XHTML certainly requires more discipline than HTML, which was notoriously tolerant of sloppy coding.
XHTML 1.0 will be superseded by XHTML 2.0, which the W3C described as "a general purpose markup language for representing documents for a wide range of purposes across the web". Version 2.0 is not fully compatible with XHTML 1.0, which has annoyed some advanced users.
Where did it originate?
HTML began in 1995 as the W3C's answer to incompatibility problems between different suppliers' browsers. It is based on SGML (Standard Generalised
Markup Language), but is much simpler.
XML is also an offspring of SGML; it keeps the richness of the language but makes it simpler to use.
What is it for?
The W3C said XHTML does not attempt to be all things to all people by supplying every possible markup idiom; it aims to supply a generally useful set of elements.
XHTML is also intended to be used in conjunction with tag sets from other XML vocabularies.
What makes it special?
Benefits of XHTML include reduced authoring costs, cleaner and more rigorous code and the ability to integrate HTML with other XML applications.
How difficult is it to master?
The W3C recommended that beginners should learn XHTML rather than HTML. Experienced HTML authors will find the learning curve short - you are supposed to be able to pick it up in your spare time, or in about a week.
Where is it used?
XHTML will replace HTML over time, but with billions of HTML pages in use, that will take many years.
What systems does it run on?
HTML and XHTML will run on all internet-enabled devices with user interfaces.
What is coming up?
There will be no further development of HTML or XHTML 1.0.
The W3C's HTML working group's efforts are now directed towards XHTML 2.0, but the W3C has proved to be responsive to requests from users - and their protests.