title: xsd for a tag that allows string content by deafult and child tags in case the attribute is specified
body: <p>Can we define xsd that allows the following two xmls</p>
  
  <p>1) If no attribute is specified , it should allow string content only </p>
  
  <p><code>&lt;tagname&gt;
  String content
  &lt;/tagname&gt;</code></p>
  
  <p>2)If the attribute "encrypted=true" is defined it should have additional child tags </p>
  
  <p><code>&lt;tagname encrypted="true"&gt;
  &lt;value&gt; encrypted content &lt;/value&gt;
  &lt;certificate&gt; version string &lt;/certificate&gt;
  &lt;/tagname&gt;</code></p>
  
  <p>Thank you !</p>