title: xmln:tns and targetNamespace
body: <p>I am seeing some XSD schema documents that declare both a <code>targetNamespace</code> and an <code>xmlns:tns</code> attribute in their top <code>schema</code> element. E.g. the following one taken <a href="http://blog.bdoughan.com/2011/12/reusing-generated-jaxb-classes.html">from here</a>. They also seem to have the same string value. I understand the role of <code>targetNamespace</code> but what does <code>xmlns:tns</code> do on top of that?</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;schema
      xmlns="http://www.w3.org/2001/XMLSchema"
      targetNamespace="http://www.example.org/Product"
      xmlns:tns="http://www.example.org/Product"
      elementFormDefault="qualified"&gt;
  ...
  </code></pre>