Writing a GUI Framework

Cmyr wrote an article about the complexity of writing a modern GUI framework. It is a great list of the complexity encompassing a proper "GUI" framework. I feel like text / rich text / unicode alone is a huge project (if you include editing, especially of large documents).

However, one thing not mentioned in this list (which I feel is only becoming more important) is that a modern GUI framework also might want to support iPad / iOS / Android.

This complexifies the undertaking by a huge amount as the differences between macOS/win/linux are much smaller than the distance between, say, iOS and macOS. Apple has been going into this direction with SwiftUI where the same code can be run on different systems and behaves differently depending on the platform. However, by doing so, this "common denominator" of all platforms automatically reduces the flexibility of the framework as every "component" needs to be cut wide enough to intelligently behave correctly per platform.