where can I find the script generate the minirootfs in branches like edge?

[braindevices]

I know there are tools like apline-make-rootfs can do similar thing. after I try out several combination I found the closest thing is ./alpine-make-rootfs --branch edge -p apk-tools -p alpine-keys. But comparing the the downloaded file, I found the script actually removed the empty dir like /home, /mnt, etc and there is no way to turn this step off. So I wonder where is the actual command or script is used to generate those rootfs in this repo? It would be nice if we include this info in the document or at least point out where we can find this info.