Eternity Skybox Viewpoint?

[Emperor S P O O N]

I'm creating a WAD in GZDoombuilder, and while scrolling through the Things menu I noticed a thing called Eternity Skybox Viewpoint. I had assumed it was another skybox viewpoint that stretched the room forever like a room of mirrors. However, when I tested it out in the level, the skybox defaulted to F_SKY1. What is an Eternity Skybox Viewpoint, and how do I get it to work? 

[Gez]

You can ignore it, it's just a thing that can be used with a bit of compatibility glue to load Eternity Engine levels in GZDoom and have them kinda work (depending on which features they use).