title: how can I write a schema that produce an unordered xml with extension
body: <p>In the following schema I am trying to make an unordered xml that extends simpleConfigurationObject:</p>
  
  <pre><code>&lt;xs:complexType name="forTestingConfigurationObjectCreator"&gt;
    &lt;xs:complexContent&gt;
      &lt;xs:extension base="simpleConfigurationObject"&gt;
        &lt;xs:all&gt;
          &lt;xs:element name="a" type="xs:string"/&gt;
          &lt;xs:element name="b" type="xs:string" minOccurs="0"/&gt;
        &lt;/xs:all&gt;
      &lt;/xs:extension&gt;
    &lt;/xs:complexContent&gt;
  &lt;/xs:complexType&gt;
  
  &lt;xs:complexType name="simpleConfigurationObject"&gt;
    &lt;xs:all&gt;
      &lt;xs:element name="base" type="xs:string" minOccurs="0"/&gt;
    &lt;/xs:all&gt;
  &lt;/xs:complexType&gt;
  </code></pre>
  
  <p>But I get the following error on the xs:all
  <b><em>"all is not the only particle in the group, or is being used as an extension"</em></b> (which is correct)</p>
  
  <p>Off-course if put the base element inside the xs:all and not use xs:extension at all I will get an unordered schema restriction. (but that is not what I want)</p>
  
  <p>The question is: how can I produce unordered schema with the extension?</p>
  
  <p>Thanks</p>