title: XSD assert not recognised
body: <p>I have an XSD where I want to use an <code>xs:assert</code> statement. The issue is I don't know how to make the assert functionality available to me. I am using Visual Studio to write it, and it gets a blue line saying it doesn't support the assert element. </p>
  
  <p>My XSD looks like this:</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
             xmlns="http://www.client.co.uk/quote" 
             targetNamespace="http://www.client.co.uk/quote" 
             elementFormDefault="qualified" 
             attributeFormDefault="unqualified"&gt;
  
  &lt;xs:element name="ProductType" type="ProductCodeType"/&gt;
    &lt;xs:simpleType name="ProductCodeType"&gt;
      &lt;xs:annotation&gt;
        &lt;xs:documentation&gt;Client Product Type&lt;/xs:documentation&gt;
      &lt;/xs:annotation&gt;
      &lt;xs:restriction base="xs:string"&gt;
        &lt;xs:enumeration value="L" /&gt;
        &lt;xs:enumeration value="C" /&gt;
        &lt;xs:enumeration value="H" /&gt;
      &lt;/xs:restriction&gt;
    &lt;/xs:simpleType&gt;
  
    &lt;xs:element name="BenefitBasisType"&gt;
      &lt;xs:simpleType&gt;
        &lt;xs:annotation&gt;
          &lt;xs:documentation&gt;Client benefit basis type&lt;/xs:documentation&gt;
        &lt;/xs:annotation&gt;
        &lt;xs:assert test= "if (ProductType = 'L') then $value = 'M' else if (ProductType = 'C') then $value = 'F' else if (ProductType = 'H') $value = 'P'" /&gt;
        &lt;xs:restriction base="xs:string"&gt;
          &lt;xs:enumeration value="M" /&gt;
          &lt;xs:enumeration value="F" /&gt;
          &lt;xs:enumeration value="P" /&gt;
        &lt;/xs:restriction&gt;
      &lt;/xs:simpleType&gt;
    &lt;/xs:element&gt;
  &lt;/xs:schema&gt;
  </code></pre>