Web Design in a Nutshell, 2nd Edition

XHTML Document Declarations

Every XHTML file must begin with declarations that tell the browser which versions of XML and XHTML are used in the document. The browser uses this information to display the document correctly. In Chapter 9 we saw how a DOCTYPE declaration can be added to the beginning of an HTML document. For XHTML, this element is required.

The following is a minimal XHTML document:

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

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>
<title>Title is required</title>
</head>

<body>
..content of document...
</body>

</html>

Let’s look at this sample one element at a time. The document begins with an XML declaration (beginning with <? and ending with ?>) that tells the XML processor that the document uses XML Version 1.0.^[11] The encoding attribute specifies the 8-bit Unicode character set (the most common). Be sure that the encoding value matches the character set used in your document (see Chapter 7 for more information on character sets).

The next element is the DOCTYPE declaration (the same as we’ve seen in XML and even regular HTML documents) that references the Transitional DTD, both by a public identifier and via a URL. If your document follows the strict XHTML version, use this declaration:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> ...