SSH -o option?

https://docs.gitlab.com/ee/ssh/ suggests using

ssh-keygen -o -t rsa -b 4096 -C "email@example.com"

to create an RSA SSH key.

However, there exists no option -o for ssh-keygen (at least not on my system or in the documentation I was able to find quickly). I don't know which option it is supposed to be.

See, for example, http://man7.org/linux/man-pages/man1/ssh-keygen.1.html