title: How to check value exists in XSLT
body: <p>I have some xml like this;</p>
  
  <pre><code>&lt;formErrors&gt;
      &lt;value&gt;address_1&lt;/value&gt;
      &lt;value&gt;address_2&lt;/value&gt;
  //.. etc
  </code></pre>
  
  <p>And in an XSL template I have $formErrors as a variable and I want to check if a value exists. If there was a PHP equivalent, I would want an in_array() function. How can I do this in XSLT?</p>