title: Why can't I call FirstOrDefault on Descendants("XName")
body: <p>Why can't I call <code>FirstOrDefault()</code> on this XML, whereas I have other <code>XDocument</code>s where <code>FirstOrDefault()</code> is available?</p>
  <pre><code>        var actual = new XDocument(
              new XComment(&quot;This is a comment&quot;),
              new XElement(&quot;Root&quot;,
                           new XElement(&quot;Child1&quot;, &quot;data1&quot;),
                           new XElement(&quot;Child2&quot;, &quot;data2&quot;)
                  ));
  
          actual.Descendants(&quot;Child1&quot;). &lt;- FirstOrDefault does not show up.
  </code></pre>