asp.net-range-validator

ASP.NET RangeValidator can't do even the most basic math !?!?!?

I'm having an issue with my ASP.NET RangeValidator controls. I want to allow users to enter a discount amount, and this amount must be negative (< $0.00). I want to verify that the amount entered in a textbox is a negative value, so I have this in my page markup: <asp:TextBox ID="tbxDiscount" runat="server" /> <asp:RangeValidator ID="r...