Choose Layer > Add Layer > Add Container Layer... to create a new Container layer.
The new Container layer can be selected from the Layers listbox to make it the active layer.
The container layer is useful in situations where you would like to animate several layers at the same time. When you move, rotate or scale a container layer, all layers that are attached to this container layer are automatically moved, rotated and scaled as well.
You can attach layers to a container layer by making that container layer the active layer, followed by choosing submenus of the Layer > Attach Layer menu item.
The container layer does not render anything, it only groups layers together. And when you delete a container layer, all attached layers are deleted as well.
The position of the container layer.
The rotation of the container layer.
The size of the container layer.
The transparency of the container layer.