XHTML Basics

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XHTML is a W3C Recommendation that represents the future of HTML. Based on HTML 4.0, XHTML is designed to be compatible with existing web browsers while complying fully with XML. This means that a properly written XHTML document is always a well-formed XML document. Furthermore, XHTML documents must adhere to one or more of the XHTML DTDs, therefore XHTML pages can be validated using today's XML parsers such as Apache's Crimson.

XHTML is designed to be modular; therefore, subsets can be extracted and utilized for wireless devices such as cell phones. XHTML Basic, also a W3C Recommendation, is one such modularization effort, and will likely become a force to be reckoned with in the wireless space.

Here is an example XHTML document:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0
Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1- strict.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>Hello, World!</title>
</head>
<body>
<p>Hello, World!</p>
</body>
</html>

Some of the most important XHTML rules include:

  • XHTML documents must be well-formed XML and must adhere to one of the XHTML DTDs. As expected with XML, all elements must be properly terminated, attribute values must be quoted, and elements must be properly nested.

  • The <!DOCTYPE ...> tag is required.

  • Unlike HTML, tags must be lowercase.

  • The root element must be <html> and must designate the XHTML namespace as shown in the previous example.

  • <head> and <body> are required.

The preceding document adheres to the strict DTD, which eliminates deprecated HTML tags and many style-related tags. Two other DTDs, transitional and frameset, provide more compatibility with existing web browsers but should be avoided when possible. For full information, refer to the W3C's specifications and documentation at http://www.w3.org.



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