One of the interesting features of the Addition control, is that it
may provide a description about its functionality. To provide a description of the
Addition control functionality, the Addition needs to have the appendDescription
method in javascript implemented. To display this description, another addition
control needs to be added to the Leaf control. This addition is called
the BubbleTooltipAddition.
BubbleTooltipAddition renders a span element that displays a box with
the data about an element when mouse is over and hides this box when the mouse is
out.