https://ru.wikipedia.org/w/index.php?title=%D0%92%D0%B8%D0%BA%D0%B8%D0%BF%D0%B5%D0%B4%D0%B8%D1%8F:%D0%A4%D0%BE%D1%80%D1%83%D0%BC/%D0%9D%D0%BE%D0%B2%D0%BE%D1%81%D1%82%D0%B8/Flow&action=history
I accidentally clicked the save button (12:21), then press again to understand that the question (as it is in the visual editor) "You want to save changes?" not shown (12:22)
then from history I click undo on the revision 12:21 (-717)
was displayed:
I click "save description" and the page says "Description has no content. Some content is required to save a description."