pg_log_fatal vs pg_log_error

Can anyone please give me a hint (and possibly add some comments to the code)
when pg_log_fatal() should be used in frontend code and when it's appropriate
to call pg_log_error()? The current use does not seem very consistent.

I'd expect that the pg_log_fatal() should be called when the error is serious
enough to cause premature exit, but I can see cases where even pg_log_error()
is followed by exit(1). pg_waldump makes me feel that pg_log_error() is used
to handle incorrect user input (before the actual execution started) while
pg_log_fatal() handles error conditions that user does not fully control
(things that happen during the actual execution). But this is rather a guess.

-- 
Antonin Houska
Web: https://www.cybertec-postgresql.com