var ScrollSpy = new Class({
			
			/* implements */
			Implements: [Options,Events],
		
			/* options */
			options: {
				min: 0,
				mode: 'vertical',
				max: 0,
				container: window,
				onEnter: $empty,
				onLeave: $empty,
				onTick: $empty
			},
			
			/* initialization */
			initialize: function(options) {
				/* set options */
				this.setOptions(options);
				this.container = $(this.options.container);
				this.enters = this.leaves = 0;
				this.max = this.options.max;
				
				/* fix max */
				if(this.max == 0) 
				{ 
					var ss = this.container.getScrollSize();
					this.max = this.options.mode == 'vertical' ? ss.y : ss.x;
				}
				/* make it happen */
				this.addListener();
			},
			
			/* a method that does whatever you want */
			addListener: function() {
				/* state trackers */
				this.inside = false;
				this.container.addEvent('scroll',function() {
					/* if it has reached the level */
					var position = this.container.getScroll();
					var xy = this.options.mode == 'vertical' ? position.y : position.x;
					/* if we reach the minimum and are still below the max... */
					if(xy >= this.options.min && xy <= this.max) {
							/* trigger Enter event if necessary */
							if(!this.inside) {
								/* record as inside */
								this.inside = true;
								this.enters++;
								/* fire enter event */
								this.fireEvent('enter',[position,this.enters]);
							}
							/* trigger the "tick", always */
							this.fireEvent('tick',[position,this.inside,this.enters,this.leaves]);
					}
					else {
						/* trigger leave */
						if(this.inside) 
						{
							this.inside = false;
							this.leaves++;
							this.fireEvent('leave',[position,this.leaves]);
						}
					}
				}.bind(this));
			}
		});