This page contains objects (iframe, flash & embedded video) that would 'reload' if hidden and then re-shown – as when a layout-pane closes and opens.
To prevent that, the slideOffscreen animation just moves the pane offscreen instead. So if a video is playing when you 'close' a pane, it will continue to play.
To use the animation, just include the jquery.layout.slideOffscreen-1.1.js (minified) file and specify "slideOffscreen" as the fxName for any panes you want to use it for.
If you enable the "useOffscreenClose" pane-option, then initHidden and initClosed also use the offscreen technique.
$("body").layout({
west__fxName: slideOffscreen // for 'closing'
, west__useOffscreenClose: true // for 'hiding'
});