Block construction in PL/pgSQL is extended by optional autonomous keyword. It is possible to treat the whole function body as an autonomous transaction:

create function foo(x integer) returns integer as $$
begin autonomous
  return x;
end;
$$ language plpgsql;

or create separate begin-end block:

create or replace function myaudit() returns boolean as $$
begin autonomous
        begin autonomous
        insert into audit_schedule values ('new audit',now());
        end;
        ... -- do audit itself
        return true;
end;
$$ language plpgsql;

When exception is raised inside BEGIN AUTONOMOUS block, this autonomous transaction is aborted and standard exception handling procedure is started, unwinding stack and executing exception handlers until exception is caught. So exception handling is done in the same way as with normal Postgres Pro subtransactions.

When an error is caught by an EXCEPTION clause, the local variables of the PL/pgSQL function remain as they were when the error occurred, but all changes to persistent database state within the block are rolled back.