title: Create XML doc by LINQ, add xmlns,xmlns:xsi to it
body: <p>I try to create an GPX XML document by LINQ to XML.</p>
  
  <p>Everything works great, except adding xmlns, xmlns:xsi attributes to the doc. By trying it different way I get different exceptions.</p>
  
  <p>My code:</p>
  
  <pre><code>XDocument xDoc = new XDocument(
  new XDeclaration("1.0", "UTF-8", "no"),
  new XElement("gpx",
  new XAttribute("creator", "XML tester"),
  new XAttribute("version","1.1"),
  new XElement("wpt",
  new XAttribute("lat","7.0"),
  new XAttribute("lon","19.0"),
  new XElement("name","test"),
  new XElement("sym","Car"))
  ));
  </code></pre>
  
  <p>The output should also contain this:</p>
  
  <pre><code>xmlns="http://www.topografix.com/GPX/1/1" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd"
  </code></pre>
  
  <p>How can I add it by Linq to XML? I tried several ways but it does not work, exceptions during compile time.</p>