System.Xml.Linq Root.Descendants vs Root.Elements

70-487 WCF (Windows Communication Foundation) Web Services

In the book Exam Ref 70-487 page 99 exemple Root.Descendants vs Root.Elements

using System;
using System.Linq;
using System.Xml.Linq;
using Microsoft.VisualStudio.TestTools.UnitTesting;
 
namespace UnitTest
{
    [TestClass]
    public class XmlTest
    {
        [TestMethod]
        public void DescVsElemReturnsSameCounts()
        {
            string documentData = @"
            <Customers>
                <Customer>
                    <FirstName>Bill</FirstName>
                </Customer>
                <Customer>
                    <FirstName>Joe</FirstName>
                </Customer>
            </Customers>";
 
            XDocument docSample = XDocument.Parse(documentData);
 
            var descendantsQuery = 

            from desc in docSample.Root.Descendants("Customer") 

            select desc;
 
            Int32 descendantsCount = descendantsQuery.Count();
            Console.WriteLine("desc :" + descendantsCount);

            // desc : 2 
 
            var elementsQuery    = 

            from elem in docSample.Root.Elements("Customer")
            select elem;

            Int32 elementsCount = elementsQuery.Count();
            Console.WriteLine("elem :" + elementsCount);

            // elem : 2 
        }
 
        [TestMethod]
        public void DescVsElemWithNestedElementReturnSameCount()
        {
            string documentData = @"
<Root>
    <CustomerName>
        <FirstName>John</FirstName>
   </CustomerName>
   <CustomerName>
        <FirstName>Bill</FirstName>
   </CustomerName>
   <CustomerName>
        <Other>
            <Another>
               Blah
            </Another>
        </Other>
        <FirstName>Joe</FirstName>
        <MiddleInitial>Q</MiddleInitial>
        <LastName>Joe</LastName>
   </CustomerName>
</Root>";
 
            XDocument docSample = XDocument.Parse(documentData);
 
            var descendantsQuery = 

            from desc in docSample.Root.Descendants("CustomerName") 

            select desc;
 
            Int32 descendantsCount = descendantsQuery.Count();
            Console.WriteLine("desc :" + descendantsCount);

            // desc : 3
            var elementsQuery = 

            from elem in docSample.Root.Elements("CustomerName")
            select elem;

            Int32 elementsCount = elementsQuery.Count();
            Console.WriteLine("elem :" + elementsCount);

            // elem : 3
        }
 
        [TestMethod]
        public void DescVsElemWithSameNestedElementReturnDifferents

Count()
        {
            string documentData = @"
<Root>
    <CustomerName>
        <FirstName>John</FirstName>
   </CustomerName>
   <CustomerName>
        <FirstName>Bill</FirstName>
   </CustomerName>
   <CustomerName>
        <Other>
            <CustomerName>
               Blah
            </CustomerName>
        </Other>
        <FirstName>Joe</FirstName>
        <MiddleInitial>Q</MiddleInitial>
        <LastName>Joe</LastName>
   </CustomerName>
</Root>";
 
            XDocument docSample = XDocument.Parse(documentData);
 
            var descendantsQuery = 

            from desc in docSample.Root.Descendants("CustomerName") 

            select desc;
 
            Int32 descendantsCount = descendantsQuery.Count();
            Console.WriteLine("desc :" + descendantsCount);

            // desc : 4 
            var elementsQuery = 

            from elem in docSample.Root.Elements("CustomerName")
            select elem;
            

            Int32 elementsCount = elementsQuery.Count();
            Console.WriteLine("elem :" + elementsCount);

            // desc : 3 
        }
    }
}

elem doesn't investigates the child elements