References are used to place a character, object or atrezzo object on a scene. An object can have several references, in one single scene or in several and different scenes. Each reference has it own conditions, which indicate when the referenced element is visible on the scene. When the conditions of a reference are met or are active (or always if the reference has no conditions) the element will appear on the scene. The position in the scene and scale depends as well of the reference and not of the referenced element, so any element can appear multiple times in the same scene but in different positions and different scales.
The references uses a layer system for the painting. They will be painted in the order indicated by the layers. That means that, when there is more than one reference, the one in the layer X will stay in front of the one in the layer Y, where Y < X, and behind the one in the layer Z, where Z > X. The layers system gives a huge flexibility to allow the creation of scenes, allowing to the create choosing when each of the elements will be painted.