How did openfl managed to build itself from defunct as3 how exactly it ported it

Hi am a new to haxe and don’t know haxe currently (originally I am a Python and Zig dev) I was impressed by the Idea of openfl long ago but due to lesser interest in gui and game making I didn’t spent time on it.

But the Idea and success of openfl & lime always inspired me a lot,
I would like to know how haxe developers managed to port the bulk of as3 libs to haxe using openfl and how exactly that no one been able to do.

And what as a zig dev I can learn from it to build such kind of game engine and gui libs for it ? As zig laks them. But haxe is not at all related to c and zig so I face problems understanding this great libs.

In general I would like to know how exactly haxe dev managed to do it and what as a zig dev I can learn to bring such power to zig.
Thanks in advance