<script runat="server">
sub submit(sender As Object, e As EventArgs)
if Page.IsValid then
lbl.Text="The page is valid!"
else
lbl.Text="The page is not valid!"
end if
end sub
</script>
<!DOCTYPE html>
<html>
<body>
<form runat="server">
Enter a US zip code:
<asp:TextBox id="txtbox1" runat="server" />
<br><br>
<asp:Button text="Submit" OnClick="submit" runat="server" />
<br><br>
<asp:Label id="lbl" runat="server" />
<br>
<asp:RegularExpressionValidator
ControlToValidate="txtbox1"
ValidationExpression="\d{5}"
EnableClientScript="false"
ErrorMessage="The zip code must be 5 numeric digits!"
runat="server" />
</form>
</body>
</html>