// JavaScript Document

window.onload = function(){
	var timer;
	var elem = document.getElementById('elem');
	var elem1 = document.getElementById('elem1');
	var elem2 = document.getElementById('elem2');
	elem2.innerHTML = elem1.innerHTML;
	timer = setInterval(Scroll,30);
	function Scroll(){
		if(elem.scrollTop>=elem1.offsetHeight){
			elem.scrollTop -= elem1.offsetHeight;
		}else{
			elem.scrollTop += 1;
		}
	}
	
	elem.onmouseover = function(){
		clearInterval(timer);
	}
	
	elem.onmouseout = function(){
		timer = setInterval(Scroll,30);
	}
	//此例看上去滚动的是elem1 , elem2中的元素，其实不是，只有elem1中的元素在滚动。elem2只是起到一个过渡作用！
}