io.BufferedRWPair doc warning may need clarification

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-10-26.05:19:33.715>
labels = ['type-bug', '3.7', 'docs']
title = 'io.BufferedRWPair doc warning may need clarification'
updated_at = <Date 2019-10-26.05:30:22.117>
user = 'https://bugs.python.org/rgov'

bugs.python.org fields:

activity = <Date 2019-10-26.05:30:22.117>
actor = 'rgov'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-10-26.05:19:33.715>
creator = 'rgov'
dependencies = []
files = []
hgrepos = []
issue_num = 38595
keywords = []
message_count = 2.0
messages = ['355404', '355405']
nosy_count = 5.0
nosy_names = ['pitrou', 'benjamin.peterson', 'stutzbach', 'docs@python', 'rgov']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue38595'
versions = ['Python 3.7']