مساعدة اريد توضيح التعامل مع xml

كود :
Dim settings As XmlWriterSettings = New XmlWriterSettings()



    Dim writer As XmlWriter





    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click

        settings.NewLineOnAttributes = True

        settings.Indent = True





        writer = XmlWriter.Create("C:\Info.xml", settings)





        writer.WriteStartDocument()

        writer.WriteStartElement("Info")





        For a = 1 To 3





            writer.WriteStartElement(String.Format("mm{0}", a))

            writer.WriteElementString("Name", String.Format("Name={0}", a))

            writer.WriteElementString("Age", String.Format("Age={0}", a))

            writer.WriteElementString("Subject", String.Format("Subject={0}", a))

            writer.WriteElementString("Avg", String.Format("Avg={0}", a))



            writer.WriteEndElement()

        Next

        writer.WriteEndElement()

        writer.WriteEndDocument()

        writer.Close()



    End Sub



    Private Sub Button2_Click(sender As System.Object, e As System.EventArgs) Handles Button2.Click



        Dim Reader As New XmlDocument

        Reader.Load("C:\Info.xml")

















        Dim mm As XmlElement = Reader.CreateElement("mm4")

        Dim Name As XmlElement = Reader.CreateElement("Name")

        Name.InnerText = "Name=4"





        Dim Age As XmlElement = Reader.CreateElement("Age")

        Age.InnerText = "Age=4"



        Dim Subject As XmlElement = Reader.CreateElement("Subject")

        Subject.InnerText = "Subject=4"



        Dim Avg As XmlElement = Reader.CreateElement("Avg")

        Avg.InnerText = "Avg=4"







        mm.AppendChild(Name)

        mm.AppendChild(Age)

        mm.AppendChild(Subject)

        mm.AppendChild(Avg)





        Reader.DocumentElement.AppendChild(mm)



        Reader.Save("C:\Info.xml")













    End Sub