Side note that these Emacs shortcuts also work on iOS pretty much everywhere (you even get it for free in completely custom text renderers, so long as you adopt the UITextInput protocol)

How are you using the modifier keys in iOS?

Just connect a Bluetooth keyboard.

Sometimes I use an iPad plus Bluetooth keyboard for writing.

What's annoying is that keyboard shortcuts mostly work in apps, but are sometimes buggy, because I think they're so rarely tested.

Not just Emacs, but anything that uses readline or similar libraries. Most shells for example.

https://en.wikipedia.org/wiki/GNU_Readline

https://github.com/chzyer/readline/blob/master/doc/shortcut....

I mean, readline shortcuts are also based on Emacs ones.

Always assumed it was the other way around without any particular evidence.

Yep. Yank and Kill work too, among others