Layers are listed in order from lowest to highest, highest being displayed on top.

Background

Background layer. It is cached so you cannot reload it by pressing F3+2. Instead you have to go to another screen and come back.

Underlay

No special effect.

Decorations

No special effect.

Overlay

This layer is the only screen that can receive custom input handlers (AddInputCallback). Note that that does not include CodeMessageCommand, CodeMessageCommand works on any layer.

Tweening on this layer will lock input until the tween is completed.

In

OnCommand for this layer is activated when you enter this screen.

Out

OnCommand for this layer is activated when your screen is about to exit.

Cancel

Only shown when a screen is cancelled. CancelCommand for this layer is activated when a screen is cancelled, which is usually when back is pressed. See CancelCommand for more information and other uses.