Container are launchers with a special attribute : They are like drawers, so you can group similar applications (launchers) which will only appear when you go over the container. You can even create a container inside a container and create a tree structure.
You create a container the same way you create a launcher for an application. You just have to tick the last box to indicate that it is a Container rather than an application. A new sub dock will be created and associated with that container. Initially you can't see it as it is empty so you have to create launcher to put in it as explained before. You can also of course just drag and drop applications on the Container
To move a launcher from one container to another one easy way is to edit the Launcher (Right Click the icon and choose "Modify Launcher") and change the name of the container in the Container field to point towards the new container (the main dock is called "_MainDock_").
Add/Remove visual effect with Compiz-Fusion
Compiz-Fusion set visual effect by default to the predefined windows types. You can also apply specific effect to the opening and closing of the dock and subdocks.
Open CCSM (Compiz Config System Manager) and go the to option of the Animation plugin; in the "Open Animation" tab. Here we are going to create a new variable which will allow us to affect a specific effect when you open a window (Compiz-Fusion considers a sub-dock like a window)
Click "Add" an choose your effect in the list from "Open effect".
Add "name=cairo-dock" in the field "xxx" (don't know the exact name in english )
Get this value to show at the top of the list. Now Compiz-Fusion will apply that specific effect only to the windows called "cairo-dock". So all sub-dock opening will use that effect. Create the same effect in the "Close Animation" tab and while you are at it go to "Focus Animation" and create a variable there as well, but here select no effect. Name it cairo-dock again. This will make sure that no effect is triggered when you fly over the dock (focus). This can create an ugly flash if not
Open Animation: Zoom effect with a duration of 250 Close Animation: Vaccuum effect with a duration of 250
Compiz Widget Layer
Go to the CCSM (CompizConfig settings manager) and to Widget Layer menu. In Comportment, add this rule
class=Cairo-dock & type=utility
After that, just do a right click on an desklet and active the Compiz Widget Layer option.
A shortcut to show/hide the dock
You can use CD in a unusual way (with a shortcut that you have set in the Accessibility menu) :
Or if you want to hide the dock without moving : (>= Cairo-Dock 3.0.0)
Active the DBus plug-in with the config panel.
Create a new launcher in the dock or what you want with the command (to hide the dock) :
Add a new shortcut on your system (with the CCSM (Compiz Config Settings Manager) if your use Compiz (in the Commands menu) or with Gnome (Shortcuts menu) or KDE, etc.) and use this command to show the dock