2.6 CDATA Sections


When an XML document includes samples of XML or HTML source code, the < and & characters in those samples must be encoded as &lt; and &amp; . The more sections of literal code a document includes and the longer they are, the more tedious this encoding becomes. Instead you can enclose each sample of literal code in a CDATA section . A CDATA section is set off by <![CDATA[ and ]]> . Everything between the <![CDATA[ and the ]]> is treated as raw character data. Less-than signs don't begin tags. Ampersands don't start entity references. Everything is simply character data, not markup.

For example, in a Scalable Vector Graphics (SVG) tutorial written in XHTML, you might see something like this:

 <p>You can use a default <code>xmlns</code> attribute to avoid having to add the svg prefix to all your elements:</p> <pre><![CDATA[        <svg xmlns="http://www.w3.org/2000/svg"             width="12cm" height="10cm">          <ellipse rx="110" ry="130" />          <rect x="4cm" y="1cm" width="3cm" height="6cm" />        </svg>      ]]></pre> 

The SVG source code has been included directly in the XHTML file without carefully replacing each < with &lt; . The result will be a sample SVG document, not an embedded SVG picture, as might happen if this example were not placed inside a CDATA section.

The only thing that cannot appear in a CDATA section is the CDATA section end delimiter , ]]> .

CDATA sections exist for the convenience of human authors, not for programs. Parsers are not required to tell you whether a particular block of text came from a CDATA section, from normal character data, or from character data that contained entity references such as &lt; and &amp; . By the time you get access to the data, these differences will have been washed away. No code you write should depend on the difference between them.

XML in a Nutshell
XML in a Nutshell, Third Edition
ISBN: 0596007647
EAN: 2147483647
Year: 2003
Pages: 232

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