This page contains probably what most of us are looking for: https://www.gnu.org/software/recutils/manual/A-Little-Exampl...

It somewhat looks like a predecessor of YAML with some kind of header integrating some schema or so.

This is one of the first thing I saw when I first started going on Hacker News. That wwas 2 years ago, when Covid was still nCov. Time really flies by. Past threads:

GNU Recutils - https://news.ycombinator.com/item?id=22153665

GNU Recutils – Tools and libraries to access plain-text databases - https://news.ycombinator.com/item?id=9320808

Recutils – Tools and libraries to access plain text databases called Recfiles - https://news.ycombinator.com/item?id=15302035