| When an XML document includes samples of XML or HTML source code, the < and & characters in those samples must be encoded as < and & . 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 < . 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 < and & . 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. | 