looking for info about repo files

i was looking at some of the sources files
i noticed that some have different formats
where should i look for details about required format for repo files

https://ftp.debian.org/debian/dists/bookworm/main/source/Sources.xz
https://ftp.debian.org/debian/dists/bookworm-updates/main/source/Sources.xz

apologies if this is the wrong list
i wood appreciate it if you would point me in the right direction