I think what you are looking for is right there on the Docs page.
-> Properties
->
-> open - (boolean) Indicates whether the slide element is visible.
-> Examples
->
-> // Hides the Element, then brings it back in with toggle and
finally alerts
-> // when complete:
-> var mySlide = new
Fx.Slide('container').hide().toggle().chain(function(){
-> alert(mySlide.open); //Alerts true.
-> });use the .open it should return true or false
