This demo is very useful when a site uses requested popup windows to display enlarged images when these images are of different dimensions. Only 1 popup is opened at all times. If the link is clicked again, then the same popup is just brought back (NOT closed, re-created and re-loaded all over again like many sites do) on top of its opener. If another enlarged image is "called", then the previous window is closed (there is no other way to do this because of different dimensions of requested popups) and the new popup window is created and loaded.
Thursday the 12th