title: Checkbox kind of fields with XML Schema
body: <p>I have the following piece of XSD:</p>
  
  <pre><code>&lt;xsd:complexContent&gt;
      &lt;xsd:extension base="mes:Request"&gt;
           &lt;xsd:sequence&gt;
             &lt;xsd:element name="empId" type="xsd:string"/&gt;
             &lt;xsd:element name="empTaskId" type="xsd:int"/&gt;
             &lt;xsd:element name="empStateName" type="xsd:string"/&gt;
             &lt;xsd:element name="empTypeName" type="xsd:string"/&gt;
             &lt;xsd:element name="empActionName" type="xsd:string"/&gt;
             &lt;xsd:element name="empTransactionId" type="xsd:int"/&gt;                               
          &lt;/xsd:sequence&gt;
      &lt;/xsd:extension&gt;
  &lt;/xsd:complexContent&gt;
  </code></pre>
  
  <p>What I want, is to allow only one field as mandatory from any of the fields listed into <code>&lt;sequence&gt;</code>. I tried using <code>&lt;choice&gt;</code> but it behaves like radio buttons; I want the functionality of check boxes (1 or more fields - multiple choice).</p>
  
  <p>Can any one help me on how to achieve this?</p>