So this looks a lot like XAML[1] for WPF (Windows Presentation Foundation)[2] to me. and I'm actually quite surprised that this was not the case for iOS development from the beginning! (declaimer: I never touched native iOS development before as a 100% Microsoft technologies professional)

[1] https://en.wikipedia.org/wiki/Extensible_Application_Markup_... [2] https://en.wikipedia.org/wiki/Windows_Presentation_Foundatio...