title: Override back button windows phone 7
body: <p>I am developing an app in windows phone 7.8 which opens a webpage in it. I have to navigate inside that page. </p>
  
  <p>I want that while pressing the back button, it goes back inside that webpage but each time I press it, the app closes. </p>
  
  <p>How can I modify the behaviour of that button? Is it possible?</p>