The BufferedLayerMapBean is a BufferedMapBean with an additional image buffer that holds Layers designated as background layers. The additional image buffer is a BufferedLayer that this MapBean manages, and all background layers are added to the BufferedLayer, which is automatically added to the bottom of the map. When layers are added to the MapBean via the setLayers() method, the Layer.getAddAsBackground() flag is checked, and if that is true for a layer, it is added to the BufferedLayer. The background layers do not receive mouse events.
It should be cautioned that the appearance of the map may not match the layer stack as it is delivered to the MapBean because of this flag. If, for example, layers 1 and 4 are marked as background layers, while layers 2 and 3 are not (in a 4 layer stack), then the map will show layers 2, 3, 1, 4, with layers 1 and 4 being displayed from the BufferedLayer. Something to think about when it comes to designing GUI elements.