It appears this was added to display "tombstones" of deleted notices.
However, it has other side-effects and the concept of keeping them visible has
not been adopted by the wider fediverse.
This was to keep the following two commits readable
- actions/showstream.php
- actions/userbyid.php
- lib/modules/ActivityHandlerModule.php
- lib/modules/ActivityHandlerPlugin.php
- lib/notices/conversationnoticestream.php
- lib/notices/noticelistitem.php
- lib/notices/noticestream.php
- lib/notices/threadednoticelistitem.php
