var ScrollSpy=Class.create();ScrollSpy.prototype={initialize:function(options){this.options=Object.extend({container:window,min:0,max:0,mode:"vertical"},options||{});this.container=$(this.options.container);this.enters=this.leaves=0;this.inside=false;var self=this;var getScrollTop=function(){return(window.pageYOffset)?window.pageYOffset:(document.documentElement&&document.documentElement.scrollTop)?document.documentElement.scrollTop:document.body.scrollTop};this.listener=function(event){if(event){event.stop()}var xy=getScrollTop();if(xy>=self.options.min&&(self.options.max==0||xy<=self.options.max)){if(!self.inside){self.inside=true;self.enters++;self.options.onEnter(xy,self.inside,self.enters,self.leaves,event)}if(self.options.onTick){self.options.onTick(xy,self.inside,self.enters,self.leaves,event)}}else{if(self.inside){self.inside=false;self.leaves++;if(self.options.onLeave){self.options.onLeave(xy,self.leaves,event)}}}};this.addListener()},start:function(){Event.observe(this.container,"scroll",this.listener)},stop:function(){Event.stopObserving(this.container,"scroll",this.listener)},addListener:function(){this.start()}};