title: How to know when a user scrolls past a <div>?
body: <p>I'm building something where I show users items that they haven't seen.</p>
  
  <p>Each item is in a <code>&lt;div&gt;</code>, so when the user scrolls past a div, or views the div, I want that item to be marked as having been seen.</p>
  
  <p>Google reader does this, if you scroll past an item in your feed there it automatically marks it as read.</p>
  
  <p>How can this be tracked? Advice please.</p>
  
  <p>Note: It shouldn't be restricted to using the mouse to scroll, hitting page down/up, using arrow keys, etc should also be counted. The main criteria is that the user has seen a div.</p>