Apps ROM flashing internals and process

[keratos]

Is there a guide that explains the internals and processes around ROM flashing. I dont mean the user process (i.e. get a .ZIP, copy to SD, reboot into clockwork recovery and install from ZIP), I mean the Android internal processes and procedures, framework, etc. that I could use to develop my own flashing code, or is this completely under the control of the O/S.
I know there is code out there, but I'd like to do this myself to gain a full understanding.
Thanks