Chapter 1. XHTML Fundamentals

At first glance, XHTML documents are very similar to HTML documents. Much of what has changed is in the background. Instead of being based on SGML (the Standard Generalized Markup Language) as HTML is, XHTML is an application of XML, the Extensible Markup Language. Because of this, several fundamental changes have been made to the way you write XHTML content as compared to how you would author content in HTML.

The W3C was actually quite concerned about the transition that needed to take place between HTML and XML. In May of 1998 they held a public workshop on the topic near San Francisco, California. During the two-day event, Web developers, software vendors, and authors of both the HTML and XML recommendations discussed how HTML could be brought into the XML world while minimizing the learning curve. The solution suggested was a transitional language that would provide a "bridge" between HTML and XML. That language is what we now know as XHTML.

XTHML conforms to the XML concept of well-formedness, which restricts the author to a complete and ordered syntax. This really isn't anything new that wasn't in HTML, just that this time it's being enforced where completeness was at times optional before. In addition to well-formedness, XML also introduces several new attributes that appear on elements in the document head section. We'll explore each of those and get a quick overview of the structural concepts for all XHTML documents.

This chapter teaches you:

• The three document types in XHTML 1.0

• XML namespaces

• How to handle language defaults

• How to add meta information

• The differences between block-level and inline elements