<com:TContent ID="Content"> <h1>Conditional Validation (clientside + server side)</h1> <div> <div> <com:TTextBox ID="text1" /> <com:TRequiredFieldValidator ID="validator1" ControlToValidate="text1" ErrorMessage="*" ControlCssClass="required"/> <com:TTextBox ID="text2" /> <com:TRequiredFieldValidator ID="validator2" ControlToValidate="text2" OnValidate="check_validate" ErrorMessage="*" ControlCssClass="required"> <prop:ClientSide.OnValidate> sender.enabled = $('#<%= $this->check1->ClientID %>').get(0).checked; </prop:ClientSide.OnValidate> </com:TRequiredFieldValidator> <com:TCheckBox ID="check1" /> </div> <com:TButton ID="submit1" Text="Submit" /> </div> </com:TContent>