GitHub has peek and go to definition in markdown and code

I don't know when this feature was released but I only noticed it today!

Pretty sweet: https://imgur.com/LLym3HS

Example repo where I notice it is enabled: https://github.com/expressjs/session

EDIT: seems like it has been out for several months but only on a few repo: https://github.blog/changelog/2019-06-11-jump-to-definition-in-public-repositories/