Understanding pg_xlog

Hello,

I am trying to understand the way in which PostgreSQL creates, updates
and uses the transaction log.

I browsed through the sources and what I understand is that, when we
"initdb", the "initdb" binary reads postgres.bki which is created by
genbki.sh.

But I fail to understand how data is stored (written) in the
"000001xxxxx" file. I came across some CRC and compression code.

I used a hexeditor to deciphar the contents of "000001xxxx" file but
it was not of much help.

Are the query (inserts/updates) put as is in the transaction log file ?

Does the CRC and compression logic transform the query ?

While we do a recovery, does it backtrace these CRC and compression
logic to retrieve the query ?

Thanks,
Shinga