Radio控件选中取消 (JS)

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<script>
function uncheck(obj)
{
    var radio=obj;
    if (radio.tag==1)
    {
        radio.checked=false;
        radio.tag=0;
    }
    else
    {
        radio.checked=true;
        radio.tag=1
    }
}
</script>
<BODY>
<input type="radio" id="rad" name="abc" onclick="uncheck(this);"/>
</BODY>
</HTML>