How to achieve multiple layers to leader scene background?

[Antagonise]

I want to achieve the effect of multiple layers to the leaderscene background, and have been looking through other mods that do this. They all include multiple background files (XX_LEADER_1, XX_LEADER_2, etc.) but I cannot find any reference to this in the files of any of them. The only related piece of code I was able to find was <SceneLayers>. I've imported all my layers, what's the next step?

 

[greyTiger]

Don't know myself but would also appreciate what the secret is as I am looking at creating some civilizations myself.