In XML, what are the nodes with question marks called, and how do I add them in C#?

Here's an example of an XML file created in InfoPath:

  <?xml version="1.0" encoding="UTF-8"?>
  <?mso-infoPathSolution solutionVersion="1.0.0.1" productVersion="12.0.0" PIVersion="1.0.0.0" href="file:///C:\Metastorm\Sample%20Procedures\InfoPath%20samples\Template1.xsn" name="urn:schemas-microsoft-com:office:infopath:Template1:-myXSD-2010-07-21T14-21-13" ?>
  <?mso-application progid="InfoPath.Document" versionProgid="InfoPath.Document.2"?>
  <my:myFields xmlns:my="http://schemas.microsoft.com/office/infopath/2003/myXSD/2010-07-21T14:21:13" xml:lang="en-us">
    <my:field1>hello</my:field1>
    <my:field2>world</my:field2>
  </my:myFields>

What are those top 3 nodes with the question mark called... and how do I create them in C#?

So far I have this:

  XmlDocument xmldoc;
  XmlDeclaration xmlDeclaration;

  xmldoc=new XmlDocument();
  xmlDeclaration = xmldoc.CreateNode(XmlNodeType.XmlDeclaration, "", "") as XmlDeclaration;
  xmlDeclaration.Encoding = "UTF-8";
  xmldoc.AppendChild(xmlDeclaration);

This works fine for the top XML declaration node , but how do I create the next two?

Thanks in advance :)