News -- XHTML: Bridging HTML & XML

It is only fitting that HTML, the language that drives the web, is in a constant state of flux. Just as the web is continually growing, changing, and maturing, HTML continues to evolve. Even with the best of intentions from standards groups and browser manufacturers, it seems HTML cannot stand still.

The early years of the web were wild and woolly, with new tags being defined by every new browser version that came along. Standards were de facto only, and early attempts to create an all-encompassing HTML standard collapsed under the sheer weight of all the features under consideration.

HTML 3.2 brought a bit of sanity to the web author's world, bringing together the most common tags and their attributes. The general, if grudging, acceptance of HTML 3.2 led to the creation of HTML 4.0, the first good, clean, well-supported HTML standard. Not only does HTML 4.0 tell you which tags are correct, it also tells you which tags are on their way out, so you can plan accordingly.

Only a year ago, the HTML world had settled comfortably into version 4.0. However, just minutes after the World Wide Web Consortium put a bow on HTML 4.0, it decided that more modularity, more flexibility, and broader capabilities were needed. So, although HTML 4.0 may be the end of one long road to standardization, it has launched a new journey for web authors that begins with XHTML 1.0.

When HTML was originally conceived, no one had any idea it would be so successful or be asked to handle so many kinds of documents, browsers, and media. While it has beared up admirably under the demands of web users, HTML 4.0 has stretched as far as it can to accommodate new technology. While HTML 4.0 is petering out, XHTML 1.0 stands ready to step in, designed to handle almost anything web authors can dream up.

While HTML is a static markup language with a fixed set of tags, XHTML is just one set of tags defined with XML, the Extensible Markup Language. Using XML, you can define tags to represent almost any kind of data or document, not just what the HTML designers had in mind when they crafted HTML. Need to capture musical notation? Chemical formulae? Integrated circuits? XML can handle all this and let you integrate your new markup tags with XHTML, creating hybrid documents that will still work with existing browsers. By adding XSL (Extensible Style Sheets), you can even teach browsers how to display all your new tags.

XML is a platform for growth and expansion of the web. XHTML is a reformulation of HTML 4.0 using XML, allowing XHTML to be integrated with all the new tools that will be XML-based. Unfortunately, fluency in HTML does not guarantee your expertise in XHTML. While XHTML made every effort to be identical to HTML, there are enough differences to cause headaches for the unsuspecting web author. The only way to stay current, capable, and fluent in XHTML is to stay atop the latest HTML 4.01 standard and augment that knowledge with all the details of XHTML. And that's exactly why we wrote the fourth edition of HTML & XHTML: The Definitive Guide.

Chuck Musciano acquired a B.S. in computer science from Georgia Tech in 1982. He is now the chief information officer of the American Kennel Club in Raleigh, North Carolina where he focuses on reengineering their legacy information systems to exploit client/server technology over the Internet. Chuck has written on UNIX- and Web-related topics in the trade press for the past decade and is now the "Tag of the Week" columnist for Web Review . He can be reached at cmusciano@aol.com.