We will probably rename AutoHideContainer to AutoHideHost to remove confusion with the properties like AutoHideLeftContainers.
Actually AutoHideLeftContainers, etc. are collections of ToolWindowContainers. Each container is a "group" of tabs in auto-hide.
The AutoHideContainer (to be named AutoHideHost) is really just a primitive that you will never use directly. It is the control that basically is directly within the DockSite in its template and hosts the four tabstrips along the sides. Its content is an implicitly-created DockHost.
The DockHost is the root control that supports a tool window hierarchy. But this too is implicitly created so you never need to worry about it.