Consistent state for pg_dump and pg_dumpall

The documentation for pg_dump says that dump files are created in a
consistent state.

Is that true across multiple tables in the same pg_dump command?
(Obviously it would not be true if I dumped tables using separate pg_dump
commands. But if I put the database into a backup state using
'pg_start_backup', would separately executed pg_dump commands be in a
consistent state across the set of dump files?)

The documentation for pg_dumpall does not say that its dump file is in a
consistent state (eg, across all tables), but it does say that it uses
pg_dump to dump clusters. So, how consistent are the tables in pg_dumpall
files?
--
Mike Nolan