title: jquery ui draggable - how can I prevent dragging outside the top of my document?
body: <p>I've set up a jquery draggable, which can be moved around the entire document, it's not contained by anything, and this is acceptable, as when the user drags, I want them to be able to drag as far down the page (or left or right) as they wish. </p>
  
  <p>Indeed, the only restriction I want - is that they should be prevented dragging the element outside of the top of the page.</p>
  
  <p><strong>Is it possible to prevent dragging outside only one edge of a container?</strong></p>