title: Changing Java EE 6 app's servlet version from 2.5 to 3.0 critical?
body: <p>We have a Java EE 6 application for which I realized we still have the Servlet version set to 2.5 (Java EE 5) instead of 3.0 (Java EE 6) in web.xml:</p>
  
  <pre><code>&lt;web-app version="2.5"
           xmlns="http://java.sun.com/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
           metadata-complete="true"&gt;
  </code></pre>
  
  <p>After:</p>
  
  <pre><code>&lt;web-app version="3.0"
           xmlns="http://java.sun.com/xml/ns/javaee"
           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
           xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
           metadata-complete="true"&gt;
  </code></pre>
  
  <p>Someone then complained that this might have side effects and must be considered a critical change (e.g. for testing/preproduction).</p>
  
  <p><strong>Question(s):</strong></p>
  
  <ol>
  <li>Is this change really critical?</li>
  <li>If so, what makes this change "critical", that is what could go possibly go wrong?</li>
  </ol>
  
  <p>I have doubts, because I think that only downgrading could be a problem...</p>
  
  <p>Thanks</p>