postgresql documentation for developers

Hi,
I am pavan working in database systems lab in Indian Institute of
science. As my M.E project I am trying to add new join type to postgresql.

I am searching on net for documentation for developers which will
describe the software architecture of postgres and tell what each
structure of postgres contains and what info the functions expect as input
etc.. which will be useful in hacking the postgresql code.

Is there any documentation of above type available? If so please
give the details.

Thanks,

regards,
pavan.

P.Pavan Kumar Chowdary
M.E(C.S)
Room no:1F19(new block)
Indian Institute of Science
Banglore.
ph no:9886501432