title: What does <![CDATA[]]> in XML mean?
body: <p>I often find this strange <code>CDATA</code> tag in <code>XML</code> files:</p>
  
  <pre><code>&lt;![CDATA[some stuff]]&gt;
  </code></pre>
  
  <p>I have observed that this <code>CDATA</code> tag always comes at the beginning, and then followed by some stuff.</p>
  
  <p>But sometimes it is used, sometimes it is not. I assume it is to mark that <code>some stuff</code> is the "data" that will be inserted after that. But what kind of data is <code>some stuff</code>? Isn't anything I write in XML tags some sort of data?</p>