logging.config: '.' (dot) as a key is not documented

[okapies]

BPO	39914
Nosy	@vsajip, @okapies

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-03-09.15:59:34.252>
labels = ['3.8', 'type-feature', '3.7', '3.9', 'docs']
title = "logging.config: '.' (dot) as a key is not documented"
updated_at = <Date 2020-03-09.16:02:04.687>
user = 'https://github.com/okapies'

bugs.python.org fields:

activity = <Date 2020-03-09.16:02:04.687>
actor = 'xtreak'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2020-03-09.15:59:34.252>
creator = 'Yuta Okamoto'
dependencies = []
files = []
hgrepos = []
issue_num = 39914
keywords = []
message_count = 1.0
messages = ['363744']
nosy_count = 3.0
nosy_names = ['vinay.sajip', 'docs@python', 'Yuta Okamoto']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39914'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9']

[okapies]

I noticed that Configurators in logging.config module accepts '.' (dot) as a key to fill attributes for filters, formatters, and handlers directly like the following:

handlers:
syslog:
class: logging.handlers.SysLogHandler
.:
ident: 'app-name: '

cpython/Lib/logging/config.py

Line 742 in 46abfc1

props = config.pop('.', None)

But it seems this functionality is not documented in https://docs.python.org/3/library/logging.config.html