csplit stand for context split, iirc.
there is also the split command. it splits on the basis of number of lines, which can be specified in various ways.
didn't know about the '--filter' flag earlier. it allows you to filter each output file through some other command. useful.
https://blog.robertelder.org/intro-to-split-command/
https://man7.org/linux/man-pages/man1/split.1.html
I gotta reserve a weekend to go through this vast and humoristisk set of knowledge.
Thank you Robert!