{{msg-mw|Revdelete-radio-set|notext=1}}

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.

Screenshot of the interface

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").

 Done. Thank you for the screenshot and explanation. Information added to relevant messages.