Create a Library that can include child control

Hi,
I would like to do somethings like following:
<AAA.Panel runat="server">
<AAA.Textbox...>
<AAA.Checkboxlist...>
<AAA.Dropdownlist...>
</AAA.Panel>
I have some idea on creating AAA.Textbox, AAA.Checkboxlist, AAA.Dropdownlist using CompositeControl. However, I have no idea on creating AAA.Panel. How can I create AAA.Panel using CompositeControl which allow me to add self-defined control to the panel?