title: XMLReader is unknown
body: <p>Following this <a href="http://csharp.net-tutorials.com/xml/reading-xml-with-the-xmlreader-class/" rel="nofollow noreferrer">introduction</a> one can use the XMLReader class by importing the namespace <code>System.Xml</code>. In my Visual Studio project I use .NET 4.0, but <code>System.Xml</code> is unknown:</p>
  
  <blockquote>
    <p>Error 1   The type or namespace name 'Xml' does not exist in the
    namespace 'System' (are you missing an assembly reference?)</p>
  </blockquote>
  
  <p>In my code I wrote:</p>
  
  <pre><code>using System.Xml;
  </code></pre>
  
  <p>What I am missing?</p>