See https://www.mediawiki.org/wiki/Project:Sandbox for example:
That page says:
Retrieved from "https://www.mediawiki.org/w/index.php?title=Project:Sandbox&oldid=3963051"
That should be only visible on the printable view. On wmf.41 vector it is visible everywhere
That text appears to be just plain text just before category links inside #bodyContent