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Limiting Allowable Values
RadTextBox can be used with RegularExpressionValidator to validate the input for a specific format.
The following example shows how to use this approach to use RadTextBox for entering Email addresses:
ASPNET
<telerik:RadTextBox RenderMode="Lightweight" ID="RadTextBox1" runat="server">
</telerik:RadTextBox>
<asp:RegularExpressionValidator
id="emailValidator"
runat="server"
Display="Dynamic"
ErrorMessage="Please, enter valid e-mail address."
ValidationExpression="^[\w\.\-]+@[a-zA-Z0-9\-]+(\.[a-zA-Z0-9\-]{1,})*(\.[a-zA-Z]{2,3}){1,2}$"
ControlToValidate="RadTextBox1">
</asp:RegularExpressionValidator>
<br/>
<asp:Button ID="Button1" runat="server" OnClick="Button1_Click" Text="Submit" />
When the user clicks the Submit button, the text box is validated and the error message is displayed if the entered text does not match the email format.