title: jQuery get the location of an element relative to window
body: <p>Given an HTML DOM ID, how to get an element's position relative to the window in JavaScript/JQuery?  This is not the same as relative to the document nor offset parent since the element may be inside an iframe or some other elements.  I need to get the screen location of the element's rectangle (as in position and dimension) as it is currently being displayed.  Negative values are acceptable if the element is currently off-screen (have been scrolled off).</p>
  
  <p>This is for an iPad (WebKit / WebView) application.  Whenever the user taps on a special link in an <code>UIWebView</code>, I am supposed to open a popover view that displays further information about the link.  The popover view needs to display an arrow that points back to the part of the screen that invokes it.</p>