Template Editor
The template editor appears as the lower area in the RadToolTip at design-time. You can drag controls from the toolbox to the RadToolTip Template Editor:
Elements placed in the template editor will show up within the ASP.NET markup RadToolTip tags:
<telerik:RadToolTip RenderMode="Lightweight" ID="RadToolTip1" runat="server" TargetControlID="HyperLink1"
Position="BottomCenter">
My Content:<asp:Button ID="Button1" runat="server" Text="Button" />
</telerik:RadToolTip>
The template content will display in the tooltip at runtime: