XHTML 1.0 and 1.1: Current Ideas and New Directions

XHTML 1.0 is the reformulation of HTML as an XML application. This means that documents as well as syntax must conform strictly to the concepts and DTDs of the language version. The ideas from HTML 4.0, especially the separation of document structure from presentation and issues concerning accessibility and internationalization, are intact in XHTML 1.0. What’s more, the three DTD offerings (strict, transitional, and frameset) originally from HTML 4.0 and later refined by HTML 4.01 are essentially the same DTDs found in XHTML 1.0.

XHTML 1.0 is best seen as a transitional language that helps puts professional Web authors in the position of writing specification-oriented markup. It puts browser manufacturers on the hot-seat and tells them “get your acts together!” It also moves us toward the extensible intelligence of XML and away from the limitations of HTML.
But transition also means that readying yourself for XML is very important, too. Fortunately, XHTML contains enough of each to help strengthen your HTML skills and to get those of you unfamiliar with XML more comfortable with its applications. Several of the primary XML concepts introduced in XHTML 1.0 are as follows:

Reintroducing structure back into the language. Picking up on the SGML and XML idea that documents should be written in conformance with the rules set out within the languages, XHTML insists upon a variety of syntax and semantic rules that must be adhered to. One such rule is the idea of well-formed.

Providing authors with incentives to validate documents. The validation of documents is somewhat controversial for a number of reasons. Certain people believe that validation is an unnecessary part of the process so long as the documents are well-formed. However, I personally feel that validation is a powerful learning tool that helps us find our mistakes, fix them, and in the process, understand the way a specific DTD works. Validation, therefore, is encouraged throughout.

Accommodating New Devices. Part of the drive to accommodate XML in the Web development environment has to do with an intriguing phenomenon. If the 90s were the years of information explosion and the movement of the PC from the workplace to the home, this decade will be known for the movement away from the desktop.

With XHTML 1.1, the concept of separation of structure and presentation is complete. XHTML 1.1 has only one public DTD, based on the Strict DTD found in XHTML 1.0. Web authors also have the option to work with modularization. Modularization breaks HTML down into discrete modules such as text, images, tables, frames, forms, and so forth. The author can choose which modules he or she wants to use and then write a DTD combining those modules into a unique application. This is the first time we really see the extensibility introduced by XML at work, because instead of having only the public DTDs to choose from, authors can now create their own applications.