Introduction to XHTML:
Why do we need XHTML?
So What's Wrong with HTML?
HTMLis the set of codes (the "markup language") that a writer puts into a document to make it displayable on theWorld Wide Web. HTML (HyperText Markup Language) has been thelingua francaof theWorld Wide Websince its inception in 1990. It has gone through several revisions, and is now at version 4. Although it has been enormously successful, the language is no longer suitable as a basis for the deployment of commercial and industrial web-based applications on theInternetandintranets.
HTML will not go through another revision, except as an application of XML, i.e. XHTML. HTML has been enormously successful and I fully expect XHTML to be of great interest to web developers now that it's a W3C Recommendation.
There won't be an 'HTML 5'. Why not? Well, bear in mind that HTML was originally designed for a very different environment than today's very demanding hi-tech Internet - namely, exchange of data and documents between scientists associated withCERN, the birthplace of the web. Since then the language has been hacked and stretched into an unwieldy monster, and the prevalence of sloppy markup practices makes it hard or impossible for some user agents (e.g. browsers, spiders, etc) to make sense of the web. After a decade of use and ad-hoc evolution, there is a strong need for a more extensible and more portable language.
XML(Extensible Markup Language)is a structured set of rules for how one might define any kind of data to be shared on the Web. It's called "extensible" because anyone can invent a particular set of markup for a particular purpose and as long as everyone uses it (the writer and an application program at the receiver's end), it can be adapted and used for many purposes - including, as it happens, describing the appearance of a Web page.
However, the immediate issue is to facilitate the transition from HTML for the mass of developers already familiar with HTML. That being the case, it seemed desirable to reframe HTML in terms of XML. The result is XHTML, a particular application of XML for "expressing" Web pages.
XHTML is, in fact, the follow-on version of HTML 4. You could think of it as HTML 5, except that it is called XHTML 1.0. In XHTML, all HTML 4 markup tags and attributes (the language of HTML) will continue to be supported.
With HTML, authors had a fixed set of elements to use, with no variation. Unlike HTML, however, XHTML can be extended by anyone that uses it. New tags and attributes can be defined and added to those that already exist, making possible new ways to embed content and programming in a Web page. With XHTML 1.0, authors can mix and match known HTML 4 elements with elements from other XML languages, including those developed by W3C for multimedia.
Desires to extend the functionality of the web will lead to combining HTML with other tag sets: (Synchronized Multimedia Integration Language -SMIL), mathematical expressions (MathML), two dimensional vector graphics (Scalable Vector Graphics -SVG), and metadata (Resource Description Framework -RDF).
Why would you want to use XHTML?
The usual reasons for upgrading to a new language version are to be able to take advantage of new bells and whistles, and also because problems with the earlier version have been fixed. However, XHTML is a fairly faithful copy of HTML 4, as far as tag functionalities go, so do not expect any fancy new tags.
The reasons offered byW3Careextensibilityandportability:
- Extensibility
- XML documents are required to bewell-formed(elements nest properly). Under HTML (an SGML application), the addition of a new group of elements requires alteration of the entireDTD. In an XML-based DTD, all that is required is that the new set of elements be internally consistent and well-formed to be added to an existing DTD. This greatly eases the development and integration of new collections of elements.
- Portability
- There will be increasing use of non-desktop devices to access Internet documents. By the year 2002 as much as 75% of Internet access could be carried out on these alternate platforms. In most cases these devices will not have the computing power of a desktop computer, and will not be designed to accommodate ill-formed HTML as current browsers tend to do. In fact, if these non-desktop browsers do not receive well-formed markup (HTML or XHTML), they may simply be unable to display the document.
While HTML isn't completely lacking those attributes, we're all too familiar with how painfully slow the evolution has been (relative to the pace of Internet development), and how hard it can be to make your pages work on a wide range of browsers and platforms. XHTML will help to remedy those problems.
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