Supplemental to last, a nifty thing as well—the per-app directory things in the Files app virtualizes the Documents directory associated with an app’s private-ish data container; or at least iVim makes it appears as such.

E.g. placing a file in iVim/Documents makes it appear in {container}/Documents when exploring it with netrw.

Likewise, while I can’t find any way to make Files express the concept of Unix hidden (.)files, the Files app does show a count that includes the .vim / .viminfo entries that come up when browsing through iVim itself.

This is kind of nice IMHO. If iOS just exports the thing somehow to a trusted Files app rather than making a separate directory outside the per-application containers, that makes the application directories in Files potentially a lot more useful for shuffling data around via the file manager. On the downside, I suppose, could mean Files would get a huge bullseye painted on its forehead for anyone wanting to find a way around some of the file system security.

By contrast, Android is a bit more liberal. The per-app area  (e.g. /data/...) is generally a total no-no to any other application, and apps are given explicit support for the “Shared” storage area (e.g. /sdcard) and a separate directory of their own located beneath it (e.g. /sdcard/Android/...)