XElement's NextNode

using System;//from  j a v  a2  s.c  o  m
using System.Linq;
using System.Collections;
using System.Collections.Generic;
using System.Xml;
using System.Xml.Linq;
public class MainClass {
    public static void Main() {
        XElement firstParticipant;
        XDocument xDocument = new XDocument(
         new XDeclaration("1.0", "UTF-8", "yes"),
         new XDocumentType("Books", null, "Books.dtd", null),
        new XProcessingInstruction("Book", "out-of-print"),
           new XElement("Books", firstParticipant =
           new XElement("Book",
           new XAttribute("type", "Author"),
       new XElement("FirstName", "J"),
         new XElement("LastName", "R")),
         new XElement("Book",
         new XAttribute("type", "Author"),
         new XElement("FirstName", "E"),
         new XElement("LastName", "B"))));
        Console.WriteLine(firstParticipant.NextNode);
    }
}