Historically, non-diegetic user interfaces have been the most common in the gaming industry. The key defining feature of them is that the components of the UI exist on a completely different plane than the actual 3D game space. Imagine here a heads-up display (HUD) as they are likely the most ubiquitous examples of non-diegetic user interfaces. A health bar, for example, does not exist within the 3D space that the game supposes nor can characters in-game interact with it. It is outside both the game’s narrative and space.