This documentation is written in an extended form of markdown called ASCIIdoc. Home page: https://asciidoctor.org/
The markdown editor used is AsciiDocFX. Home page: https://asciidocfx.com/
A single file with (admittedly slightly esoteric) markup can generate multiple output formats.
It's suggested you generate the .html version (which I think looks the best right now, until I figure out nicer looking PDF stylesheets).
I plan on using sections from the Image 1.2b and 2.0 documentation to save some effort. Still learning about ASCIIdoc, pull requests encouraged!
asciidoctor-pdf prg-master.adoc
asciidoctor-pdf -a pdf-theme=basic prg-master.adoc
https://github.com/asciidoctor/asciidoctor-pdf/tree/main/examples