All layers appear in the Layers list. The Layers list allows you to view and rearrange layer ordering in the Paint node, as well as select layers to be hidden or revealed.
Layers can be internal or external to the Paint node. An internal layer is a transparent layer that can only be added from the Paint node. It can be used to create, for example, an alpha.
An external layer does not originate from the Paint node. It can be an image and can include a front and/or alpha. An external layer is connected to the Paint node by means of a Layer node, whereas an internal layer needs no such connection since it originates with the Paint node. A common reason for adding an external layer is to touch up an image's front or alpha. When you paint on an external layer, you are compositing strokes onto the incoming image. This makes it possible to change the incoming image without losing your strokes.
When you add either an internal or external layer, it goes to the top of the Layers list. The order in the Layers list reflects the layer order on the canvas. The topmost layer covers the image data of the underlying layers. Layers can be hidden or rearranged within the Layers list.
When you delete a layer, it is removed from the Layers list. When you clear a layer, it remains in the Layers list but all strokes are removed.
