title: Optional AttributeGroup
body: <p>I have to define a attribute group for 2 mutually inclusive data elements. In the below example if <code>TO_DT</code> is present <code>FROM_DT</code> has to be present and <code>TO_DT</code> is not present then <code>FROM_DT</code> is not present. </p>
  
  <p>I thought of creating these as mandatory attributes and define attributegroup as optional but its not working: </p>
  
  <pre><code>&lt;xs:attributeGroup name="DateRangeAttributes" id="Element_Common_545"&gt;
    &lt;xs:attribute name="TO_DT" type="xs:date" use="required" id="Element_Common_547"/&gt;
    &lt;xs:attribute name="FROM_DT" type="xs:date" use="required" id="Element_Common_546"/&gt;
  &lt;xs:attributeGroup&gt;
  </code></pre>
  
  <p>Can anyone suggest a way to handle this using attributes </p>