The stubs have some issues so this has some generous cast
and ignores in it, but it is better than not having stubs.
Note that confusing that Element is a function which creates
_Element instances (and similarly for Comment).
There are two situations which were previously not properly checked:
1. If the requested URL was replaced with an oEmbed URL, then the
oEmbed URL was not checked against url_preview_url_blacklist.
2. Follow-up URLs (either via autodiscovery of oEmbed or to pre-cache
images) were not checked against url_preview_url_blacklist.