Thanks for the issue, I've subscribed to it.
https://github.com/jftuga/chars/issues/2
According to the page, several machines and operating systems used CR as EOL. While the systems are all obsolete, files from that era that use CR as EOL could persist and be transferred to modern systems. Clearly those are weird on modern systems, so they should be warned about in a linting situation, which I would like to use your project 'chars' in.
Having different EOL chars within the same file is definitely a thing, usually by mistake. I had to fix a bug about this recently:
https://github.com/EionRobb/purple-discord/pull/416