Modify XML parsing library descriptions to forewarn of content loss hazard

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2021-03-19.18:52:35.411>
labels = ['3.7', '3.8', '3.9', 'docs']
title = 'Modify XML parsing library descriptions to forewarn of content loss hazard'
updated_at = <Date 2021-03-19.18:52:35.411>
user = 'https://github.com/ridgerat'

bugs.python.org fields:

activity = <Date 2021-03-19.18:52:35.411>
actor = 'ridgerat1611'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2021-03-19.18:52:35.411>
creator = 'ridgerat1611'
dependencies = []
files = []
hgrepos = []
issue_num = 43561
keywords = []
message_count = 1.0
messages = ['389111']
nosy_count = 2.0
nosy_names = ['docs@python', 'ridgerat1611']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue43561'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']