* It is usually done via `canvas` widget. So that widget is needed. And this
mean just abilities to drawing in the library.
* Multithreading in GUI usually depends on a backend code. At the moment, only
Vulcan and DX12 supports multithreading, OpenGL not. If you try to update GUI
from another thread in, for example, GTK, there will be dragons. ;) Thus, the
GUI library should be backend independent either, like Nuklear or ImGUI.
* That's require to write two libraries. :) Both approaches are mutually
exclusive and require a separated code. Even a general concept how a GUI
library works is separated for both ways.
* Small size: the point 5 is against this point. Details above. ;)
Security-critical things usually require very expensive certifications. :) It
could be done, for example, by formally verified the library.
* It is doable, I saw a couple of libraries which allowed that.
