> Use memory-safe programming languages, 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;
There is absolutely zero way to satisfy the latter part here. It's at best non-enforceable. If I'm using C++ and use std::span instead of a c-style array, is that good enough?
Why not? The wording is “features that improve memory safety”
It doesn’t say that it needs to provide absolute memory safety. Based on the linked WebKit guidelines, it seems like they meet the criteria.