IVim

Boogaloo iVim is a text editor on iOS based on Vi IMproved by Bram Moolenaar.

Getting help on iVim

• Reddit, iVim HowTos.

Apple iCloud

All iCloud Documents are store in ~/Library/Mobile\ Documents/com~apple~CloudDocs. So:
Start by opening Terminal and then

$ cd ~/Library/Mobile\ Documents/com~apple~CloudDocs
$ ls -Al
.DS_Store
..
bash

• SuperUser, Access iCloud Drive via terminal.

Where are my Files

Every App on an iPad has its own local storage. So you can not edit files that live in other Apps local storage.
Can you edit files in the iCloud?

Which files can be edited.