I hope my code is useful:
<head>
<script language="javascript">
function setBehavior(oInput,sValue)
{
if (o = eval("window."+oInput)) {
o.onchange = function(){this.modify=true}
o.onfocus = function(){if(!this.modify)this.value=''}
o.onblur = function(){if(!this.modify)this.value=sValue}
}
}
function setAllInput()
{
setBehavior('theName','Your name plz !!!');
setBehavior('theEmail','Your Email plz !!!');
setBehavior('theAge','Your Age plz !!!');
}
</script>
</head>
<BODY onload="setAllInput()">
<input name="theName" value="your name plz !!!">
<input name="theEmail" value="your email plz !!!">
<input name="theAge" value="your age plz !!!">
</BODY>