title: What's the difference between <a_element /> and <a_element xsi:nil="true" />?
body: <p>do you know if there's a difference between these tags on XML/XSD?</p>
  
  <pre><code>&lt;a_element /&gt; and &lt;a_element xsi:nil="true"/&gt;
  </code></pre>
  
  <p>e.g:</p>
  
  <pre><code>&lt;SpreadCurve&gt;
        &lt;Index&gt;3M&lt;/Index&gt;
        &lt;IndexNumber&gt;4587&lt;/IndexNumber&gt;
        &lt;BusinessArea xsi:nil="true" /&gt;
  &lt;/SpreadCurve&gt;
  
  and
  
  &lt;SpreadCurve&gt;
        &lt;Index&gt;3M&lt;/Index&gt;
        &lt;IndexNumber&gt;4587&lt;/IndexNumber&gt;
        &lt;BusinessArea /&gt;
  &lt;/SpreadCurve&gt;
  </code></pre>
  
  <p>Are these <strong>equivalent</strong> ?</p>
  
  <p>If I have a XSD element:</p>
  
  <pre><code>&lt;xsd:element name="BusinessArea" type="xsd:string"/&gt;
  </code></pre>
  
  <p>this means that it is by default xsi:nil="false". And this means it will not accept a null value for this element.</p>
  
  <p>My doubt is, will it accept this one?</p>
  
  <pre><code>&lt;BusinessArea /&gt;
  </code></pre>
  
  <p>What does this really mean to the XSD?</p>
  
  <p>Best regards </p>