title: Mathematical operation with XML node values for selection
body: <p>I'm trying to use the value of an XML node to select a group of nodes, my specific problem is the following.
  I have the nodes computers with the attribute model and in their children is the node HardDrive</p>
  
  <pre><code>&lt;PC model="Lindows OSX"&gt;
      &lt;HardDrive&gt;500&lt;/HardDrive&gt;
  &lt;/PC&gt;
  </code></pre>
  
  <p>I'd like to select only the PCs which HardDrive is over 500gb, so I dont know if the function text() let's me work with numbers, something like </p>
  
  <pre><code>//parent::HardDrive[text()&gt;500]/@model
  </code></pre>