How to write into XMl at a particular node in android?

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I have a XML file like this\[code\]<?xml version="1.0" encoding="utf-8"?><Survey Name="Aerosmith's Survey" Id="S2"UserId="Admin"CreatedBy="Administrator"cultureName="en-CA" numberOfQuestions="5"completedPercent="0" createdTimeStamp="June 26, 2012 16:01" lastUpdatedTimeStamp=""><Questions><Question id="q1" name="Question #1" type="SingleChoice" allowBackButton="false" isRequired="true" numLines="0" questionIndex="1"> <QuestionText>Who is your favourite Aerosmith's Member ?</QuestionText> <Answers> <Answer answerIndex="1" >Joey Kramer</Answer> <Answer answerIndex="2" >Steven Tyler</Answer> <Answer answerIndex="3" >Tom Hamilton</Answer> <Answer answerIndex="4" >Joe Perry</Answer> <Answer answerIndex="4" >Brad Whitford</Answer> </Answers> <Response respondedTimeStamp=""></Response> <OnChoice></OnChoice> </Question> <Question id="q2" name="Question #2" type="MultipleChoice" allowBackButton="true" isRequired="true" numLines="0" questionIndex="2"> <QuestionText> Which is your favourite Aerosmith Song ?</QuestionText> <Answers> <Answer answerIndex="1" >Dream On</Answer> <Answer answerIndex="2" >Sweet Emotion</Answer> <Answer answerIndex="3" >Walk this way!!</Answer> <Answer answerIndex="4" >I Don't Want to Miss a Thing</Answer> <Answer answerIndex="5" >Jaded</Answer> </Answers> <Response respondedTimeStamp=""></Response> <OnChoice></OnChoice> </Question> <Question id="q3" name="Question #3" type="Date" allowBackButton="true" isRequired="true" numLines="0" questionIndex="3"> <QuestionText>What is Your Date of birth?</QuestionText> <Answers></Answers> <Response respondedTimeStamp=""></Response> <OnChoice></OnChoice> </Question></Questions></Survey>\[/code\]Now in my App I have used a SAX parser to read these.Now each question has a question type as you can see in my xml.\[code\]<Question id="q1" name="Question #1" type="SingleChoice" allowBackButton="false" isRequired="true" numLines="0" questionIndex="1">\[/code\]based on this I have populated my Checkbox in a list view.Now what i want to do is that suppose any user checks an item then in the tag \[code\]<Response respondedTimeStamp=""></Response>\[/code\]I have to write the time stamp and the response value as text for that particular question.So How do i do it?