[emacs-berlin] Understanding M-x

[jman]

Hello,

I was reading a suggestion about using the package `smex` in a recent configuration
https://github.com/shaneikennedy/emacs-light/blob/e454a55f6deb20feeb175d219e2f019d929e0ee0/init.el#L165

`smex` allows sorting by last used command when invoking M-x
https://github.com/nonsequitur/smex

Even if I don't have that package installed, I do have this kind of sorting so I was wondering what 
is making it happen in my config.
So I've tried C-h k M-x but as expected I got a quite generic:

    M-x runs the command execute-extended-command (found in global-map),
    which is an interactive native-compiled Lisp function in ‘simple.el’.

But the documentation or the code for that function doesn't get me closer to my goal.

Any suggestion?

Thanks