than the simple X rating. In some cases, the X ratings were applied by reviewers or film scholars, e.g. William Rotsler, who wrote "The XXX-rating is for hardcore, the XX-rating is for softcore, and an X-rating is for comparatively cool films." Nothing beyond the simple X rating has ever been officially recognized by the MPAA. Because of the heavy use of the X rating by pornographers, it became associated largely with pornographic films, so that non-pornographic films given an X rating would have fewer theaters willing to book them and fewer venues for advertising. Many newspapers refused to advertise X-rated films. This led to a number of films being released unrated sometimes with a warning that the film contained content for adults only. In response, the MPAA eventually agreed in 1990 to a new NC-17 rating that would be trademarked, and could only be applied by the MPAA itself. By trademarking the rating, the MPAA committed to defending an NC-17 film charged with violating obscenity laws. See also Censorship List of NC-17 rated films Motion Picture Production Code Strong language Television content rating system .xxx, top-level Internet domain References External links Screen Online article about the X certificate Refused Classification Website covering in varying detail many films that have run foul of the Australian Office of Film and Literature Classification, with separate sections for hardcore films and video games Explanation of X-ratings in the US How "X-rated" Came to Mean "Porn" and the Death of Movies for Grown-ups A brief history of the social and legal forces that drove adult themes out of the legitimate cinema, by film director Tony Comstock Australian government says yes to R18+ video games bill Motion picture rating systems British Board of Film Classification Motion Picture Association Self-censorship Film censorship