Some time ago I decided to write an ED clone with syntax highlighting, hired. On my way to that I found that the macro commands ('g', 'v', 'G', 'V') pretty much require that you write an ED library for them. So I did, and here it is.
I have taken some liberties in the commands I have found less than ergonomic, so especially advanced commands have some differences (both syntax and behaviour) from GNU Ed. This strives to be a list of these changes.
Currently it is based on both my experiences with hired and the hired repo specifically (a manual fork, so it has the whole history). This may well mean the API is ill suited for your use. If that is the case I'd be happy to make some changes to make it more general.
In line with this, the help text is often a bit outdated. I'll get to that, and improve on the error type, before the first stable release.
The original ED keeps track of the last line you interacted with and defaults to working on that for most commands. I felt this deserved expanding, so add-ed instead tracks the last span of lines you interacted with. My hope is that this is more intuitive. (To avoid unpleasantries such as partial saving some commands default to the whole buffer instead. Such as 'w', the save command.)
The library has been designed with clear traits to enable changing out most components easily. For example it should be somewhat easy to create a SSH/SFTP IO implementation for remote editing, or a GUI frontend implementing the UI trait.
Include and expose a simple in-memory buffer implementation
Add 'C' command. This modifies the UI trait.
This project is essentially built upon the regex crate, as regex is the heart of Ed.