Conceptual overview for GRUB2

[scl]

Hey folks,
I am currently writing my bachelor thesis about the linux boot process 
including GRUB. I am wondering if there is any conceptual 
overview/documentation for GRUB2 or anything similiar you could point me to?
Unfortunately I did not find anything other than the User and Developer 
Documentation and Multiboot Specification but like to learn about what 
procedures are used by GRUB2 to load an operating system -- just how the 
bootsequence of GRUB2 looks like.

Regards,
mooeen