Required Field Validator
Code:
<RequiredFieldValidator Type="string" ControlRef="@Name" Text="Name is required." ErrorMessage="Name is required but in summary!" />
<RegularExpressionValidator ValidationExpression="^[0-9]{5}$" ControlRef="@Name" Text="Not a 5 digit number." />
<AspNetValidationSummary Font_Bold="true" DisplayMode="BulletList" HeaderText="Please fix these errors:" />