title: What is the vim groupname of the '<? ?>' tag in an xml file?
body: <p>I am doing my own colorscheme and I would like to customize the  tag from XML files.</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  </code></pre>
  
  <p>But I can't find the name of the groupname.</p>
  
  <p>Any one knows it ?</p>