title: xsd select multiple values from enumeration or equivalent type
body: <p>I have the following XSD sample</p>
  
  <pre><code>&lt;xs:element name="days" minOccurs="0"&gt;
      &lt;xs:simpleType&gt;
          &lt;xs:restriction base="xs:string"&gt;
              &lt;xs:enumeration value="Monday"/&gt;
              &lt;xs:enumeration value="Tuesday"/&gt;
              &lt;xs:enumeration value="Wednesday"/&gt;
              &lt;xs:enumeration value="Thursday"/&gt;
              &lt;xs:enumeration value="Friday"/&gt;
              &lt;xs:enumeration value="Saturday"/&gt;
              &lt;xs:enumeration value="Sunday"/&gt;
          &lt;/xs:restriction&gt;
      &lt;/xs:simpleType&gt;
  &lt;/xs:element&gt;
  </code></pre>
  
  <p>The xml extract should be able to contain multiple values from the list but restrict what they enter to the enumeration above, for example, &lt;days&gt;Saturday, Wednesday&lt;/days&gt;. Is this possible?</p>