title: Specify sorting in lists of elements in XML Schema
body: <p>Is there a way to specify in an XML Schema that the elements of a list must appear sorted by some text nodes?</p>
  
  <p>E.g.:</p>
  
  <p>I want to craft an xsd for which the following xml is valid:</p>
  
  <pre><code>&lt;root&gt;
      &lt;Users&gt;
          &lt;User&gt;
              &lt;Id&gt;1&lt;/Id&gt;
              &lt;Username&gt;lsuarez&lt;/Username&gt;
          &lt;/User&gt;
          &lt;User&gt;
              &lt;Id&gt;3&lt;/Id&gt;
              &lt;Username&gt;dforlan&lt;/Username&gt;
          &lt;/User&gt;
          &lt;User&gt;
              &lt;Id&gt;7&lt;/Id&gt;
              &lt;Username&gt;ecavanni&lt;/Username&gt;
          &lt;/User&gt;
      &lt;/Users&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>But the following is not:</p>
  
  <pre><code>&lt;root&gt;
      &lt;Users&gt;
          &lt;User&gt;
              &lt;Id&gt;7&lt;/Id&gt;
              &lt;Username&gt;ecavanni&lt;/Username&gt;
          &lt;/User&gt;
          &lt;User&gt;
              &lt;Id&gt;1&lt;/Id&gt;
              &lt;Username&gt;lsuarez&lt;/Username&gt;
          &lt;/User&gt;
          &lt;User&gt;
              &lt;Id&gt;3&lt;/Id&gt;
              &lt;Username&gt;dforlan&lt;/Username&gt;
          &lt;/User&gt;
      &lt;/Users&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>That is, the elements in the collection appear sorted by User.Id</p>