((REVISIONUSER)) is a "magic word" that returns the last person to change an article. On November 14, 2013, this feature was expanded to include ((REVISIONUSER:(article-name))), which makes it possible to query who edited any of a number of other articles. This template does not need to be used in place of the magic word normally, but is provided so that a WP:Lua module can use frame:expandTemplate to access this function. (There may well be some other better way to do this).
Example: ((REVISIONUSER|Astronomy)) -> . (i.e. [[User:]])
But you can get this straight from the parser function by typing ((REVISIONUSER:Astronomy)).
((REVISIONUSER))
magic word (tracked in Phabricator as Task T166946) which prevents it from working properly if the user name starts with certain wiki-markup characters such as a * and possible other characters. The work-around is to wrap the call to the magic word with the nowiki function of Module:String2:
((#invoke:String2|nowiki|((REVISIONUSER))))
-> Tumbuka Arch((#invoke:String2|nowiki|((REVISIONUSER:User:***SkooterBecca***))))
-> Tumbuka Arch((#invoke:String2|nowiki|((REVISIONUSER|User:***SkooterBecca***))))
-> Tumbuka Arch