In Real Studio, it was easy to change a window to a container control, but I have been unable to do so in Xojo. When I click the edit button next to Super in the inspector and the Select Super window opens, Window is the only choice available. I am using Windows with Xojo 2014R1.
type ContainerControl in the Super field and press Tab or Return
You can’t change the super of the “main window.” Instead right click on it, select duplicate, then type in ContainerControl as the super on the duplicate window and press enter and you will have a ContainerControl version of the window.