Gets all layers in the given group
handles the changing of a layer
registers a Layer as Exclusive, the activation of a layer triggers the deactivation of all other exclusive Layers. The layer collection adds exclusive layers to the manager on adding the layer to the collection.
layer to register
Removes a layer from tracking. Layer collections remove the layer once they are removed from them.
layer to unregister
Tracks layer exclusivity, added to every LayerCollection.