How is Scene.isLoaded determined?

I cannot find anything in docs that breaks down the scene loading process and how the Scene.isLoaded property is determined.

I need to mock large scene loading and cannot find a way to delay a scene’s loading. Would be useful to understand the flow especially when needing to load external assets in the scene and only mark the scene is loaded via code.

example of how to load scene in the background and play it whenever you need

http://answers.unity.com/answers/409780/view.html