[ADMIN] synchronous_commit and wal_writer_delay

[A J]

Does a synchronous_commit force WAL to be committed to disk or does it just 
WAIT for WAL to be committed according to WAL's set frequency to write ?
i.e. if I set wal_writer_delay=200ms and set synchronous_commit=on, will each 
commit wait for upto 200ms before committing ?