Inconsistency in repeatable read
Here is my reading of that section.  I will admit it is confusing.

Suppose I have two tables:

CREATE TABLE batch (
   id serial not null unique,
   control_code text primary key,
   date_posted date not null default now()
);

CREATE TABLE details (
   batch_id int not null references batch(id),
   description text,
   primary key(batch_id, description)
);


Now, suppose we insert batch and details records in different transactions.  Session 1 inserts a batch and starts to insert details but before it finishes, session 2 starts up.  Session 2 gets to see the batch heading info, but does not wait on the commit on details to inform the user that no records are found.  Now if your batch and details are entirely in the same transaction then this never is a problem.

this would differ from serializable where you would expect to wait for the previous insert to complete and commit or rollback before determining whether to notify the user that no rows were found.