Thank you very much for the answers, Mario and Harald!
So, now, I'm wondering how I should layout several UI elements on a single screen.
I made a basic button skeleton that is capable of 9-slice like stretching. Then I put multiple of them on a single Spine project by importing the button skeleton.
![](https://dl.dropboxusercontent.com/s/ewa70d7rbst0q8j/%E3%82%B9%E3%82%AF%E3%83%AA%E3%83%BC%E3%83%B3%E3%82%B7%E3%83%A7%E3%83%83%E3%83%88%202022-01-26%2019.04.59.png?dl=0)
If I export this project for UE4 then Spine generates four skeletons. That allows me to control each of them individually.
But I'm not sure if this is a reasonable way to deal with more complicated UI since it might be a bit tedious to put many skeletons on a UMG widget one by one.
Do you have any recommendations about UI layout?