HTML & XHTML: The Definitive Guide, 6th Edition

Creating XHTML Documents

For the most part, creating an XHTML document is no different from creating an HTML document. Using your favorite text editor, simply add the markup elements to your document's contents in the right order, and display it using your favorite browser. To be strictly correct ("valid," as they say at the W3C), your XHTML document needs a boilerplate declaration upfront that specifies the DTD you used to create the document and defines a namespace for the document.

Declaring Document Types

For an XHTML browser to correctly parse and display your XHTML document, you should tell it which version of XML is being used to create the document. You must also state which XHTML DTD defines the elements in your document.

The XML version declaration uses a special XML processing directive. In general, these XML directives begin with <? and end with ?>, but otherwise they look like typical tags in your document.^[*] To declare that you are using XML version 1.0, place this directive in the first line in your document:

<?xml version="1.0" encoding="UTF-8"?>

This tells the browser that you are using XML 1.0 along with the 8-bit Unicode character set, the one most commonly used today. The encoding attribute's value should reflect the character set used in your document. Refer to the appropriate International Organization for Standardization (ISO) standards for other encoding names.

Once you've gotten the important issue of the XML version squared away, you should then declare the ...