title: WebForms, AJAX and prompt popups elegantly
body: <p>I have a web site already developed with tons of updatePanels, buttons, and integrated functionality.<br>
  I have to add some confirmation prompts, these prompts should be customized, and have options like 'Continue', 'Cancel' .<br>
  This is a possible scenario:</p>
  
  <ul><li>The user writes something in one textbox, and then clicks a submit button.</li>
  <li> The Prompt appears.</li>
  <li>When the user clicks continue the page should continue with the normal flow, and when press cancel the  submit action should be stopped. </li>
  </ul>
  
  <p>I want to be the less obtrusive possible,  What is the best approach to achieve this?</p>
  
  <p><B>EDIT:</B>  </p>
  
  <p>I can't use any library like Jquery. I can use ModalPopupExtenders, or simply styled divs.<br>
  Fundamentally the problem is when clicking this submit button, the submit action is taken and my popup does not appear, even if I add the JS function at onclick Event.<br>
  I can ClearAll submit button handlers, add the one that shows my popup, but how can I continue with the 'submit' action when the popup's 'continue' btn is clicked?</p>