ol.control.Bar is a panel that contains other controls. Control bar can be nested.
You can choose the position for the control bar.
It can group
ol.control.Toggle with a toggleOne propertie to have only one activated at a time. You can compose toolbars with it.
A sub-bar can be nested to add options/controls visible when the parent
ol.control.Toggle is active (see the
sub-bar example).