Web Design in a Nutshell, 3rd Edition

XHTML (Extensible Hypertext Markup Language)

In the context of XML, XHTML is a language for describing the content of hypertext documents intended to be viewed or read in some sort of browsing client. It uses a DTD that declares such elements as paragraphs, headings, lists, and hyperlinks. It uses the namespace http://www.w3.org/1999/xhtml.

In the context of web design, XHTML is the updated version of HTML and is the current W3C recommendation for authoring web pages. It has all the same elements and attributes as the HTML 4.01 Recommendation, but where HTML was written according to the broader rules of SGML, XHTML has been rewritten according to XML syntax. That means that XHTML documents need to be well-formed, requiring more stringent markup practices. XHTML is by far the dominant use of XML on the Web.

XHTML is discussed in great detail in Chapters 8 through 15.