function checkmail(){
if(document.youjian.useremail.value.length!=0)
  {
    if (
         document.getElementById("useremail").value.charAt(0)=="." ||        
         document.getElementById("useremail").charAt(0)=="@"||       
         document.getElementById("useremail").indexOf('@', 0) == -1 || 
         document.getElementById("useremail").indexOf('.', 0) == -1 || 
         document.getElementById("useremail").lastIndexOf("@")==document.youjian.useremail.value.length-1 || 
         ddocument.getElementById("useremail").lastIndexOf(".")==document.youjian.useremail.value.length-1)
     {
      alert("Email地址格式不正确！");
     document.getElementById("useremail").focus();
      return false;
      }
   }
 else
  {
   alert("Email不能为空！");
   document.getElementById("useremail").focus();
   return false;
   }
 }
 
 	/*startList =function()
	{
			if(document.all&&document.getElementById)
			{
				navRoot=document.getElementById("nav");
				for(i=0;i<navRoot.childNodes.length;i++)
				{
					node=navRoot.childNodes[i];
					if(node.nodeName=="LI")
					{
						node.onmouseover=function()
						{
							this.className+=" over";	
						}
						this.className=this.className.replace(" over","");
					}
				}
			}
		}
	window.onload=startList;*/