contextvars documentation unclear on thread-locality

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-03-19.07:26:24.308>
labels = ['3.8', 'type-feature', '3.7', 'docs']
title = 'contextvars documentation unclear on thread-locality'
updated_at = <Date 2019-03-19.07:26:24.308>
user = 'https://bugs.python.org/HameerAbbasi2'

bugs.python.org fields:

activity = <Date 2019-03-19.07:26:24.308>
actor = 'Hameer Abbasi2'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2019-03-19.07:26:24.308>
creator = 'Hameer Abbasi2'
dependencies = []
files = []
hgrepos = []
issue_num = 36359
keywords = []
message_count = 1.0
messages = ['338322']
nosy_count = 3.0
nosy_names = ['docs@python', 'yselivanov', 'Hameer Abbasi2']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue36359'
versions = ['Python 3.7', 'Python 3.8']