Which is why viewport values like maximum-scale, minimum-scale, and user-scalable do not work on iOS10+, no matter the browser.
The Unix workstation versions (HP-UX, AIX, etc.) were built with a commercial equivalent to Winelib: a library that implemented Win32 APIs on top of Unix and X11.
I have no idea how they managed to build the IE code on a compiler that wasn't MSVC.
So far, this is the only thing that really drives me bonkers about iOS and has for a long time. I'd love to be able to use an actual third-party browser with a third-party rendering engine, even if it meant having to install a particular signing certificate or some such. Doubly so for using browser-specific extensions. Who knows, maybe iOS 15?
(While I'm wishing for ponies, the ability to change OS-level default applications would be nice.)
I understand it would be a lot of effort for little gain. But if more developers would offer their stuff as self-signable "xcode projects" (maybe even just a .dylib and some wrapper source), it would be really cool.
Not entirely true: Every browser developer is free to use whatever engine they like on iOS. Mozilla could use Gecko, Google could use Blink. They just don’t do it, because what’s not allowed is JITs (because security), thus 3rd-party JS-engines would always be slow.
So the reason everybody uses WebKit on iOS is not that they are forbidden own engines, but only JITs, so Apples is faster.
2.5.6 Apps that browse the web must use the appropriate WebKit framework and WebKit Javascript.
The JIT thing was true, but a few years back, they lifted this restriction, see "4.7 HTML5 Games, Bots, etc." for its current incarnation which also says "your app must use WebKit and JavaScript Core to run third party software".