Beginning XML, 5th Edition

Chapter 17

XHTML and HTML 5

WHAT YOU WILL LEARN IN THIS CHAPTER:

• The relationships between XML, HTML, XHTML, and XHTML 5
• The structure of XHTML documents
• Creating XHTML with XSLT and XQuery
• Styling XHTML and XML with CSS
• The HTML 5 Open Web Platform
• Differences between HTML 5 and XHTML
• When to use which sort of HTML

The HyperText Markup Language (HTML) was introduced in 1989 as the way to create documents on the World Wide Web (WWW). The World Wide Web (Web for short) combined several ideas at the same time: it is decentralized, meaning that anyone can put up a web server without needing permission from a central authority. This decentralization allowed the Web to scale. The Web scales because it is unreliable: you can encounter broken links. Previous attempts at large-scale HyperText systems had required a single, central link database. Despite being unreliable and decentralized, the Web also gives every reachable resource a name. These names, Uniform Resource Identifiers, are commonly known as URIs, URLs, or web addresses. Any web client, such as a browser, can fetch any resource given its URI. The resources are usually fetched using the HyperText Transfer Protocol (HTTP); HTTP takes a list of formats and languages, and returns the requested resource in the best format available in the requested language. Most often, that format is HTML.

There was actually nothing special about any of the ideas in the World Wide Web, but the combination of ideas was new. For many early users, ...