Web Design in a Nutshell, 3rd Edition

XML on the Web

As mentioned earlier, XML turned out to have uses that reach far beyond web documents , but it is still the W3C’s primary tool for optimizing information exchange over the Web. XML is put to use on the Web in several ways.

The most common is XHTML, a reformulation of HTML according to the stricter syntax rules of XML. XHTML is formally introduced in the next section and is discussed in detail in the Chapters 8 through 15.

XHTML 1.1 can be combined in documents with other XML vocabularies such as MathML and SVG (Scalable Vector Graphics; discussed next). Namespaces help the parser keep track of which elements belong to which application (note that this requires a browser that supports namespaces ).

XML documents may also be displayed directly in web browsers that support XML. The "Browser Support" section provides more information on how browsers deal with XML.

Finally, one of the most widespread uses of an XML-based format for web content is in the form of RSS feeds that allow summaries of web content (or the content itself) to be shared on other sites or read with a special reader. RSS is discussed in detail in the following section.

Tip

The W3C keeps a directory of Recommended DTDs to use in web documents at http://www.w3.org/QA/2002/04/valid-dtd-list.html.