title: XSD ordering for extended type?
body: <p>I am trying to write a schema that doesn't require specific ordering for an extended type.  I tried to use an "all" group, but it seems to only permit a "sequence".</p>
  
  <p>I am getting this error message and am a bit confused.  </p>
  
  <blockquote>
    <p>An all model group must appear in a particle with {min occurs} = {max occurs} = 1, and that particle must be part of a pair which constitutes the {content type} of a complex type definition.</p>
  </blockquote>
  
  <pre><code>    &lt;complexType name="credentialElement"&gt;
      &lt;complexContent&gt;
          &lt;extension base="env:namedElement"&gt;
              &lt;all&gt;
                  &lt;element name="username" type="env:envString" minOccurs="1" /&gt;
                  &lt;element name="password" type="env:envString" minOccurs="1" /&gt;
                  &lt;element name="domain" type="env:envString" minOccurs="0" /&gt;
              &lt;/all&gt;
          &lt;/extension&gt;
      &lt;/complexContent&gt;
  &lt;/complexType&gt;
  </code></pre>
  
  <p>Eric</p>
  
  <p>EDIT:
  It seems that this is not possible.  After running this through xmlint I got a different error message:</p>
  
  <blockquote>
    <p>The type has an 'all' model group in its {content type} and thus cannot be derived from a non-empty type, since this would produce a 'sequence' model group containing the 'all' model group; 'all' model groups are not allowed to appear inside other model groups.</p>
  </blockquote>
  
  <p>Not sure if there is a clean work around.</p>