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XHTML is a Web presentation language based on HTML but recast in well-formed XML. It's designed to continue the trend in HTML 4.01 of encouraging the separation of content from presentation. Discover the many changes that XHTML 2.0 will offer, including features that will improve the ability of authors to express content structure and meaning.
XHTML 1.0 [W3C Recommendation] is mostly HTML 4 recast as well-formed XML. HTML is a Standard Generalized Markup Language (SGML) application, and when XML was developed as a simplification and specialization of SGML for the Web, HTML (itself the lingua franca of the Web) became the chief candidate for adoption to XML. The result is a variation named XHTML. The goal of the XHTML work is an HTML language for which parsing is simpler (because of XML's stricter syntax). XHTML is easily processed using off-the-shelf XML tools, and it strives to better separate content from presentation. XHTML is one of the oldest XML applications and has a huge number of contributing interests, resulting in many parts and versions.
XHTML 1.0 defines distinct Document Type Definitions (DTDs) and namespaces to correspond to the three HTML 4 DTDs -- Strict, Transitional, and Frameset. XHTML Modularization [W3C Recommendation] provides a framework for breaking down XHTML into separate modules defined as distinct DTDs. For example, all element and attribute types used for defining lists would be in one module, and element types geared toward presentation would be in another module. In this way, you can develop and refine XHTML by adding, subtracting, and updating generally independent modules. The first step along these lines was XHTML Basic [W3C Recommendation], which defines the minimum set of XHTML modules required for any language that counts as XHTML. XHTML Basic in itself could be used as the content language for Web clients such as mobile phones, personal digital assistants (PDAs), pagers, and set-top boxes. XHTML 1.1 [W3C Recommendation] is basically the XHTML 1.0 Strict DTD broken down using the module framework.
XHTML 2.0 [in development] is a rewrite of XHTML without considerations of backward compatibility with HTML. The idea is pretty much to start from scratch in developing a content language for the Web, learning from the past without being enslaved to the past. Examples of big changes include:
- Eliminating
<br/>,<img/>, and other elements considered excessively presentation-oriented - Eliminating HTML-style forms in favor of XForms
- Eliminating HTML-style linking elements in favor of HLink
- Replacing many JavaScript™-driven dynamic tasks with XML Events
- Replacing HTML-style frames with XFrames
More importantly, XHTML 2.0 makes many additions that improve the ability of authors to express content structure and meaning. Breaking backward compatibility has been controversial. Some commentators say that maintaining the (X)HTML name and bumping the revision number will lead to confusion. Others say that the changes are much needed and that XHTML is still an Extensible Hypertext Markup Language, so the name remains appropriate.
XHTML is often used with other embedded formats, such as Mathematical Markup Language (MathML), Resource Description Framework (RDF), Scalable Vector Graphics (SVG), Synchronized Multimedia Integration Language (SMIL), and Voice Extensible Markup Language (VoiceXML). Such combination documents are called multi-modal or non-monolithic. The World Wide Web Consortium (W3C), International Organization for Standardization (ISO), and other organizations are putting a good deal of effort into encouraging strong support for such documents.
- Ease into understanding of XHTML 1.x through the tutorial XHTML,
step-by-step by Uche Ogbuji (developerWorks, September 2005).
-
XHTML: The power of two languages by Sathyan
Munirathinam provides a brief introduction to XHTML 1.0 (developerWorks,
July 2002), as does XHTML
1.0: Marking up a new dawn by Molly Holzschlag (developerWorks,
February 2005).
-
The Web's future: XHTML 2.0 by Nicholas Chase is a good
overview of the changes in XHTML 2.0 (developerWorks, September 2002),
and The future of HTML, Part 2: XHTML 2.0 by Edd Dumbill
provides a tour of the different constituent specifications from which
XHTML 2.0 is built up (developerWorks, January 2006).
- In Linking in XHTML 2.0, Micah Dubinko zooms in on the
subtopic of hyperlinking, which is one of the most important parts of
any HTML-related specification (developerWorks, March 2005).
- The tutorial Modularization of XHTML by Nicholas Chase is useful for
those who want to understand the building blocks of the language
(developerWorks, October 2001).
- Read about other XML standards:
Index of XML
standards.
- Participate in any of several XML-centered forums:
XML
zone discussion forums.
- Get involved in the developerWorks community: developerWorks blogs
- Find out how you can become an IBM-Certified
Developer in XML and related technologies at IBM XML
certification.
- See the developerWorks XML Zone for a wide range of
technical articles and tips, tutorials, standards, and IBM Redbooks at
XML
technical library.
- Stay current with technology in these sessions: developerWorks technical events and webcasts.
- Build your next development project with trial
software available for download directly from developerWorks: IBM trial software
