JavaScript鼠标点符号到文本框时的提示信息 _JavaScript

JavaScript鼠标点到文本框时的提示信息
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
    "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">

<head>
  <title></title>
  <style type="text/css">
  *{
  margin:0px;padding:0px;font-size:12px;
  }
    input{
      width:100px;height:20px;border:1px solid #ccc;
    }

  </style>
</head>

<body>
<script language="javascript">
function tips(id,str){
var l=document.getElementById(id).offsetLeft;
alert(document.getElementById(id).offsetTop); alert(document.getElementById(id).clientHeight);
var t=document.getElementById(id).offsetTop+document.getElementById(id).clientHeight+5;
document.getElementById("tips").innerHTML="提示："+str;
document.getElementById("tips").style.left=l+"px";
document.getElementById("tips").style.top=t+"px";
document.getElementById("tips").style.display="";
}
function outtips(){
    document.getElementById("tips").style.display='none';
}
</script>
<div id="tips" style="position:absolute;border:1px solid #ccc;padding:0px 3px;color:#f00;display:none;height:20px;line-height:20px;background:#fcfcfc"></div>
<br />
姓名：<input type="text" id="username" onfocus="tips('username','姓名长度最多16个字符')" onblur="outtips()" />
<br />
密码：<input type="password" id="password" onfocus="tips('password','密码长度必须在3-18位之间')" onblur="outtips()" />
</body>
</html>