I dont find any instruction about how to use this Object Class in Object Parameter in any document or how to activate it, please give some clues

https://i.gyazo.com/280af7575389c419ee8f...0beae5.png

I expect it will work like decal placement, but not sure

Yes it should work like a decal, it's best used as a flat surface, like a flat quad to be placed somewhere on other flat surfaces.

But how can I setup one? It is a bit tricky to setup a cone light point light (creating Object Class > display as Point light) but there is no option like that for overlay, there is no example btw

https://i.gyazo.com/dc7cfeea90f3b58e2e7e...a03a0d.png

There is no difference between choosing Terrain Class and Overlay Class for this wall damage plane, that why I feel so confused, which is advantage of choosing Overlay than Terrain when the result is the same ?

Or there is no "In editor" Overlay object ? if so, is Overlay Class in editor useless ?

Overlay supports decals with smooth alpha blending