This is very nice. It would be interesting to see the same for other code bases like emacs and vim.

emacs is quite approachable because of its self documenting nature. In practice, if you want to drill down on a particular thing, you need to use some of the describe-* commands. For example want to know how emacs save something?

1) find the command it uses with describe-keybinding, you find the command "save-buffer"

2) "describe-command save-buffer" brings you onto the lisp world where it is defined => "files.el"

3) want to know how a variable is define within files.el? "describe-variable buffer-file-name" and now you are in C territory

4) rinse and repeat with some describe-function when needed

5) get lost onto the beauty of emacs which in my opinion is its interactive / self documenting nature which unfortunatly is not more common in all the software we use

I don't know why you're getting downvoted. It would be wonderful if there was same site for all the big open source projects