Anybody know what the question is to which 'yes' in this message is an option?
It is a part of the RevisionDelete feature. The message is a caption for a column of radioboxes inside a box with Revdelete-legend (“Set visibility restrictions”) as a title.
Set visibility restrictions
There are three radio buttons in each row, and the captions above each column read Revdelete-radio-same (“Do not change”), Revdelete-radio-set (“Hidden”), and Revdelete-radio-unset (“Visible”).
Do not change
Hidden
Visible
Done. Thank you for the screenshot and explanation. Information added to relevant messages.