Nesting controls in a user control

I am trying to create a user control that I can nest other controls in. Think like the existing panel control. I want to create some HTML structure that can be used, then nest other controls inside of this structure.
 So my aspx might look something liek this:
 <userControl:MyPanel ID="Panel1" runat="server"> some other controls in here, maybe html too </userControl:MyPanel>  Then in in my ascx may look something like this:
<table> <tr> <td> I want the nested controls and html to show up here </td> </tr> </table>  Any idea on how I can do this? Many ASP.Net controls do this. At this point I've figured that if I add tese atributes ...