// Show popup when user hovers over a child element of a container div.
$('div.child', '#container').mouseover(function() {
  $('#popup').show();
});
 
// But hide it only when the mouse pointer leaves the container. Mouseout doesn't
// work here because of event bubbling - it'll trigger on child elements of
// #container as well.
$('#container').bind('mouseleave', function() {
  $('#popup').hide();
});