How to set maximum length to Multiline TextBox in ASP.NET 2.0

First of all this is a bug in .net..We cant set MaxLength while property of TextBox is set to Multiline.
We can achieve this by using regular expression validator.
<asp:RegularExpressionValidator ID="MaxLengthValidator" ControlToValidate="AddersTxtbox" Text="Max length is 20" ValidationExpression="^[\s\S]{0,20}$" runat="server" />