It’s literally from their requirements page
https://developer.apple.com/support/alternative-browser-engi...
You have to request explicit permission to be able to be a browser on iOS. You can’t just ship an app. I assume part of that process is that you specifically demonstrate that you try your best to use best safety practices.
Again, it’s also not absolute safety. It’s just due diligence review.
Sorry if I wasn't clear. I meant the WebKit guidelines were from the commenter, not from the apple page.
> or features that improve memory safety within other languages, within the alternative web browser engine at a minimum for all code that processes web content;
This can't be analyzed in any real way, so its just another way that Apple will restrict web engines and claim it was due to "not enough use of memory safety language features"