Every crucial message element equipped with a class [[ https://codesearch.wmflabs.org/deployed/?q=errorbox&i=nope&files=&repos= | errorbox ]] or warningbox etc. shall get the ARIA attribute role="alert" as well.

Example: MediaWiki:Titleprotected‎ which shall inform that neither editing nor page creation is possible.

Reason: Screenreaders will process such elements and preface their story with such warnings rather than starting from the first beginning and page navigation, where the section with the warning may be skipped. Since blind people cannot see that there is a big red box on page they might not catch an important information. The preview warning on source editing is just some text among many other text.

The same goes for popup boxes alerting on crucial state, as generated by OOui etc. OOui needs to provide a flag. When such popup is inserted a good screenreader shall listen to DOM and tell the user.