“This is an instruction booklet that shows you how to build a text editor in C.
The text editor is antirez’s kilo, with some changes. It’s about 1000 lines of C in a single file with no dependencies, and it implements all the basic features you expect in a minimal editor, as well as syntax highlighting and a search feature.
This booklet walks you through building the editor in 184 steps. Each step, you’ll add, change, or remove a few lines of code. Most steps, you’ll be able to observe the changes you made by compiling and running the program immediately afterwards.”—https://viewsourcecode.org/snaptoken/kilo/index.html
Might be interesting to compare to the source code of mg, which is a minimal editor written in C that works like Emacs.