title: How to validate for language attributes in XSD?
body: <p>I have an XML document with language specific elements, example:</p>
  
  <pre><code>&lt;root lang="en fr"&gt;
      &lt;section&gt;
          &lt;title lang="en"&gt;English Title&lt;/title&gt;
          &lt;title lang="fr"&gt;French Title&lt;/title&gt;
          &lt;sequence&gt;2&lt;/sequence&gt;
          &lt;field&gt;
             &lt;type&gt;date&lt;/type&gt; 
             &lt;label lang="en"&gt;English field label&lt;/label&gt;
             &lt;label lang="fr"&gt;French field label&lt;/label&gt;
          &lt;/field&gt;
      &lt;/section&gt;
      &lt;section&gt;
          &lt;title lang="en"&gt;Another English Title&lt;/title&gt;
          &lt;title lang="fr"&gt;Another French Title&lt;/title&gt;
          &lt;sequence&gt;1&lt;/sequence&gt;
      &lt;/section&gt;
  &lt;/root&gt;
  </code></pre>
  
  <p>At the top, the root element is intended to declare the document defines both english and french information.</p>
  
  <p>There are certain elements in the document that need to be provided in english and french, such as <code>title</code> and <code>label</code> , since the root element declares support for both.</p>
  
  <p>Is it possible to to express such a constraint in XML Schema?  I could express the <code>root</code> element language attribute differently, such as <code>lang-en="1" lang-fr="1"</code> if that helps.  </p>