<com:TContent ID="Content"> <com:TLabel ForControl="text1" Text="Text 1:" /> <com:TTextBox ID="text1" /> <com:TRequiredFieldValidator ID="validator1" ControlToValidate="text1" ErrorMessage="Text 1 is required" /> <div> <com:TCheckBox ID="check1" Text="More..." /> </div> <com:TPanel ID="panel1" Style="display:none" > <com:TLabel ForControl="text2" Text="Text 2:" /> <com:TTextBox ID="text2" /> <com:TRequiredFieldValidator ID="validator2" ControlToValidate="text2" OnValidate="validator2_onValidate" OnPreRender="validate2_onPostValidate" ErrorMessage="Text 2 is required"> <prop:ClientSide.OnValidate> sender.enabled = $("<%= $this->check1->ClientID %>").checked; </prop:ClientSide.OnValidate> </com:TRequiredFieldValidator> </com:TPanel> <com:TButton ID="button1" Text="Submit!" /> <com:TClientScript> Event.OnLoad(function() { Event.observe("<%= $this->check1->ClientID %>", "click", function(ev) { $("<%= $this->panel1->ClientID %>").toggle(); }); }); </com:TClientScript> </com:TContent>