title: How to add values from multiple nodes from XSLT?
body: <p>Say if I have an xml document as:</p>
  
  <pre><code>&lt;nutrition&gt;
  &lt;food&gt;
  &lt;value&gt;2&lt;/value&gt;
  &lt;/food&gt;
  &lt;food&gt;
  &lt;value&gt;4&lt;/value&gt;
  &lt;/food&gt;
  &lt;/nutrition&gt;
  </code></pre>
  
  <p>Then how do I add the two values, using XSLT, like 2+4?</p>
  
  <p>I have tried sum function in XSLT, but it doesn not work in inner tags.</p>