Yes in sample it is not there. But it is fairly easy. You just need to add label and hide show it accordingly. Check the sample below
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Untitled Page</title>
<script type = "text/javascript">
function isNumeric(keyCode)
{
var r = ((keyCode >= 48 && keyCode <= 57) || keyCode == 8)
document.getElementById("<%=lblError.ClientID %>").style.display = r ? "none" : "block";
return r;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<asp:Label ID="Label1" runat="server" Text="Numeric"></asp:Label>
<asp:TextBox ID="txtNumeric" runat="server" onkeydown = "return isNumeric(event.keyCode);" onpaste = "return false;"></asp:TextBox>
<asp:Label ID="lblError" runat="server" Text="Only Numeric" ForeColor = "Red" style = "display:none"></asp:Label>
</div>
</form>
</body>
</html>
