How does this Roblox plugin make a new window in studio to view skyboxes?

While watching a video about the Roblox Studio plugin Atmos, I saw that you were able to preview skyboxes in a separate window, and I was just curious as to how this is done. I thought it might have been a viewport frame at first, but didn’t think that was the case if a new window is opened in studio, almost as if its a new instance of roblox studio?

If anyone knows how this is done i’d be interested to know. Image below for what I am referring to by a “new window” being opened to preview the skyboxes