Extension tags with no content don't have any visual representation or information in the sidebar.
Steps to reproduce
- Go to https://www.mediawiki.org/w/index.php?title=Project:Sandbox&oldid=2455494
- Copy them, and paste them into a new page being edited by VisualEditor
- Alternatively, just insert those extension tags and add an empty space in each one of them
- Press alt + shift + v (trigger diff viewer)
- Click visual
Some indication that there were nodes added to the text, either inline or in the sidebar.
Green blocks indicating added content with no way to differentiate them from each other.
Extra notes: While most tags were in fact empty and don't have a "visual" representation to speak of, the empty reference tag was invalid, and didn't display properly, while the score extension was empty until saved. It then returned an error.
See https://www.mediawiki.org/wiki/Topic:Tphpb41ld3eky7yf for more information and examples