The C1ExpanderExtender control allows you to show or hide embedded or external content within an expanding panel using various animation effects. The expanding content can be shown or hidden by clicking on the expander header at run time.
C1ExpanderExtender Markup
The following markup creates a C1ExpanderExtender control. Set the TargetControlID property to attach the extender to a control.
<cc1:C1ExpanderExtender ID="Panel1_C1ExpanderExtender" runat="server" TargetControlID="Panel1">
</cc1:C1ExpanderExtender>