What does the strange git command mean?

Question

git

Hello!
Colleagues threw the command:
git checkout -- .
No, of course I understand what it does.
But I can't figure out in which part of the documentation this is described!
How can "prefix" be used without a key at all?
I understand when they write --version, or just -v. But so that two minuses, and nothing after ...
Hmm ...