Currently, the Cite extension will render loud, red errors in the middle of article content, if there are parsing errors in the attributes. This will become an issue if we have to roll back the extends attribute support.
The main goal would be that extends errors are displayed in a less obtrusive way. It's possible that we have to change how other errors are handled as well.
Don't break the article for readers, for example show the error in the "References" section rather than in the middle of content. But this should still be visible for editors. Maybe add a property or category to the page, to make it easily discoverable.
Example of current error display:
