title: XSD: unordered list of elements with different occurs possible?
body: <p>I have an element <code>A</code> with children <code>B</code> and <code>C</code>.
  They can occur in <strong>any order</strong> but:</p>
  
  <ul>
  <li><code>B</code> should unlimited or not at all</li>
  <li><code>C</code> can occur only once or not at all</li>
  </ul>
  
  <p>I tried to do it with <code>&lt;xs:all&gt;</code> but it doesn't accept <code>maxOccurs="unbounded"</code>.</p>
  
  <p>Example Code:</p>
  
  <pre><code>&lt;?xml version="1.0"?&gt;
  &lt;xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"&gt;
      &lt;xs:element name="A"&gt;
          &lt;xs:complexType&gt;
              &lt;xs:all&gt;
                  &lt;xs:element name="B" minOccurs="0"
                              maxOccurs="unbounded" type="xs:string"/&gt;
                  &lt;xs:element name="C" minOccurs="0" 
                              maxOccurs="1" type="xs:string"/&gt;
              &lt;/xs:all&gt;
          &lt;/xs:complexType&gt;
      &lt;/xs:element&gt;
  &lt;/xs:schema&gt;
  </code></pre>
  
  <p>Is here another way to accomplish this?</p>