Grub internals?

[Kaleem Khan]

I've been trying to understand the inner workings of grub. I don't see
any documentation which explains in details how the first stage
downloads second stage's first sector, and then how this downloaded
first sector downloads the rest of the second stage, and how exactly
the second stage binary is created. Looking into the code and makefile
seems to be the only option which may take a long time. Do you have
any other suggestions?

Thanks.
Kaleem.