Every time I have reached for TOML I have ended up using JSON. The first reason is that Python standard library can read but not write TOML, which is generally useless for me. The second reason is TOML does not add any benefit over JSON. It’s not that much easier to read and IMO JSON is easier to write by hand because the syntax rules are completely obvious.
cut out a random piece of your document. is it a partial or a complete document?
paste it somewhere else in the document. you have to fix the indentation because if not then the document won't work or mean something completely different
For settings files I always have an example file with sensible values filled in and along with descriptive keys that serves as reasonable documentation. If something is truly unknowable, I’ve probably done something wrong.
In my opinion, the settings file isn’t where this information should be presented. I would put these notes in the release log and readme and example settings file. I have also written this information to logging during startup so a user knows what to do, or I write a migration that does the change automatically if that’s possible.
This is only my opinion and you can use the comment method described like “//“: “Deprecated” if desired.
The very first moment that I had to use JSON as a configuration format, and I was desperate to find a way to make a long string into a JSON field. JSON is great for many things, but it's not good at all for a configuration format where you need users to make it pretty, and need features like comments or multi-line strings (because you don't want to fix a merge conflict in a 400 character-wide line).