Above each control on the main panel is a tab marked with a triangle.
Clicking this tab displays the subpanel, whose name is indicated on its title
bar.
Subpanels contain:
A labelled copy of the control in the Main Panel.
Other controls for running applications. (You can promote
these to the Main Panel.)
An Install Icon control, which acts as a drop zone for adding
a control to the subpanel.
