This removes the wrapping box inside the anonymous content, and replaces
the anonymous label with an ::after CSS rule that sets text based on
the [title] attribute.
Because it doesn't replicate the anonymous wrapping box with light DOM:
- Calling JS don't need to be updated (the child added via appendChild
is still a direct descendant of the element).
- Many CSS selectors don't need to be updated (if they were targeting the
slotted children as direct descendants. However, CSS selectors that were
targeting the anonymous content directly do need to be updated, since those
nodes are removed.
Differential Revision: https://phabricator.services.mozilla.com/D12172
c98e0ea6ce