What does <![CDATA[]]> in XML mean?

Question

I often find this strange CDATA tag in XML files:

I have observed that this CD

Answer 1

A CDATA section is "a section of element content that is marked for the parser to interpret as only character data, not markup."

Syntactically, it behaves similarly to a comment:

... but it is still part of the document:

 < " and &
    or write things like
    
    but my document is still well formed!
]]>

Try saving the following as a .xhtml file (not .html) and open it using FireFox (not Internet Explorer) to see the difference between the comment and the CDATA section; the comment won't appear when you look at the document in a browser, while the CDATA section will:

Using a Comment




Using a CDATA Section

 & "
]]>

---

Something to take note of with CDATA sections is that they have no encoding, so there's no way to include the string ]]> in them. Any character data which contains ]]> will have to - as far as I know - be a text node instead. Likewise, from a DOM manipulation perspective you can't create a CDATA section which includes ]]>:

var myEl = xmlDoc.getElementById("cdata-wrapper");
myEl.appendChild(xmlDoc.createCDATASection("This section cannot contain ]]>"));

This DOM manipulation code will either throw an exception (in Firefox) or result in a poorly structured XML document: http://jsfiddle.net/9NNHA/