Xml – What does in XML mean

cdataxml

I often find this strange CDATA tag in XML files:

<![CDATA[some stuff]]>

I have observed that this CDATA tag always comes at the beginning, and then followed by some stuff.

But sometimes it is used, sometimes it is not. I assume it is to mark that some stuff is the "data" that will be inserted after that. But what kind of data is some stuff? Isn't anything I write in XML tags some sort of data?

Best Answer

CDATA stands for Character Data and it means that the data in between these strings includes data that could be interpreted as XML markup, but should not be.

The key differences between CDATA and comments are:

As Richard points out, CDATA is still part of the document, while a comment is not.
In CDATA you cannot include the string ]]> (CDEnd), while in a comment -- is invalid.
Parameter Entity references are not recognized inside of comments.

This means given these four snippets of XML from one well-formed document:

<!ENTITY MyParamEntity "Has been expanded">

<!--
Within this comment I can use ]]>
and other reserved characters like <
&, ', and ", but %MyParamEntity; will not be expanded
(if I retrieve the text of this node it will contain
%MyParamEntity; and not "Has been expanded")
and I can't place two dashes next to each other.
-->

<![CDATA[
Within this Character Data block I can
use double dashes as much as I want (along with <, &, ', and ")
*and* %MyParamEntity; will be expanded to the text
"Has been expanded" ... however, I can't use
the CEND sequence. If I need to use CEND I must escape one of the
brackets or the greater-than sign using concatenated CDATA sections.
]]>

<description>An example of escaped CENDs</description>
<!-- This text contains a CEND ]]> -->
<!-- In this first case we put the ]] at the end of the first CDATA block
     and the > in the second CDATA block -->
<data><![CDATA[This text contains a CEND ]]]]><![CDATA[>]]></data>
<!-- In this second case we put a ] at the end of the first CDATA block
     and the ]> in the second CDATA block -->
<alternative><![CDATA[This text contains a CEND ]]]><![CDATA[]>]]></alternative>

Related Solutions

Javascript – When is a CDATA section necessary within a script tag

A CDATA section is required if you need your document to parse as XML (e.g. when an XHTML page is interpreted as XML) and you want to be able to write literal i<10 and a && b instead of i<10 and a && b, as XHTML will parse the JavaScript code as parsed character data as opposed to character data by default. This is not an issue with scripts that are stored in external source files, but for any inline JavaScript in XHTML you will probably want to use a CDATA section.

Note that many XHTML pages were never intended to be parsed as XML in which case this will not be an issue.

For a good writeup on the subject, see https://web.archive.org/web/20140304083226/http://javascript.about.com/library/blxhtml.htm

Java – Best way to compare 2 XML documents in Java

Sounds like a job for XMLUnit

Example:

public class SomeTest extends XMLTestCase {
  @Test
  public void test() {
    String xml1 = ...
    String xml2 = ...

    XMLUnit.setIgnoreWhitespace(true); // ignore whitespace differences

    // can also compare xml Documents, InputSources, Readers, Diffs
    assertXMLEqual(xml1, xml2);  // assertXMLEquals comes from XMLTestCase
  }
}

Best Answer

Related Solutions

Javascript – When is a CDATA section necessary within a script tag

Java – Best way to compare 2 XML documents in Java

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