Buttons "Publish" and "Cancel" in right top corner are very useful. $wgOOUIEditPage from MW 1.29 is removed in MW 1.30. "Cancel" is not working properly for now: it redirects to "undefined" error page. Is there any solution to fix this problem without removing both or single button?
Topic on Extension talk:WikiEditor
"Cancel" was removed because it almost never got used. Most people (on the public wikis, especially Wikipedia) who wanted to cancel an edit either closed their browser tab or clicked on the "Read" tabs (at the very top). The team has considered other options, such as putting the "Cancel" button in one of the menus.