js 鼠标移上去显示层的效果
<script type="text/javascript">
function enableTooltips(id){
var links,i,h;
if(!document.getElementById || !document.getElementsByTagName) return;
AddCss();
h=document.createElement("span");
h.id="btc";
h.setAttribute("id","btc");
h.style.position="absolute";
document.getElementsByTagName("body")[0].appendChild(h);
if(id==null) links=document.getElementsByTagName("a");
else links=document.getElementById(id).getElementsByTagName("a");
for(i=0;i<links.length;i++){
    Prepare(links[i]);
    }
}
function Prepare(el){
var tooltip,t,b,s,l;
t=el.getAttribute("title");
if(t==null || t.length==0) t="link:";
el.removeAttribute("title");
tooltip=CreateEl("span","tooltip");
s=CreateEl("span","top");
s.appendChild(document.createTextNode(t));
tooltip.appendChild(s);
b=CreateEl("b","bottom");
l=el.getAttribute("href");
if(l.length>30) l=l.substr(0,27)+"...";
b.appendChild(document.createTextNode(l));
tooltip.appendChild(b);
setOpacity(tooltip);
el.tooltip=tooltip;
el.onmouseover=showTooltip;
el.onmouseout=hideTooltip;
el.onmousemove=Locate;
}
function showTooltip(e){
document.getElementById("btc").appendChild(this.tooltip);
Locate(e);
}
function hideTooltip(e){
var d=document.getElementById("btc");
if(d.childNodes.length>0) d.removeChild(d.firstChild);
}
function setOpacity(el){
el.style.filter="alpha(opacity:95)";
el.style.KHTMLOpacity="0.95";
el.style.MozOpacity="0.95";
el.style.opacity="0.95";
}
function CreateEl(t,c){
var x=document.createElement(t);
x.className=c;
x.style.display="block";
return(x);
}
function AddCss(){
var l=CreateEl("link");
l.setAttribute("type","text/css");
l.setAttribute("rel","stylesheet");
l.setAttribute("href","http://web-graphics.com/mtarchive/bt.css");
l.setAttribute("media","screen");
document.getElementsByTagName("head")[0].appendChild(l);
}
function Locate(e){
var posx=0,posy=0;
if(e==null) e=window.event;
if(e.pageX || e.pageY){
    posx=e.pageX; posy=e.pageY;
    }
else if(e.clientX || e.clientY){
    if(document.documentElement.scrollTop){
        posx=e.clientX+document.documentElement.scrollLeft;
        posy=e.clientY+document.documentElement.scrollTop;
        }
    else{
        posx=e.clientX+document.body.scrollLeft;
        posy=e.clientY+document.body.scrollTop;
        }
    }
document.getElementById("btc").style.top=(posy+10)+"px";
document.getElementById("btc").style.left=(posx-20)+"px";
}
</script>
<script type="text/javascript">
window.onload=function(){enableTooltips()};
</script>
<style type="text/css">
body{font: 76%/1.5 Arial,sans-serif;background: #FFF;color: #333}
div#container{width: 500px;margin:0 auto}
h1{color: #3CA3FF;margin: 1em 0 0;letter-spacing: -2px}
p{margin: 0 0 1.7em}
a{color: #F60;font-weight:bold}
a:hover{color: #F00}
</style>
<center>
<div id="container">
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</div>