1982 it was redefined as meaning "Suitable for those aged 18 and over". The X certificate was replaced in November 1982 by the 18 certificate. Sometimes the rating of a film has changed significantly over time. For example, the French film Jules and Jim received an X rating in 1962 that was reduced to a PG rating in 1991. In some cases, films with extreme political content received an X rating. The Battleship Potemkin was refused a certificate for "inflammatory subtitles and Bolshevik propaganda" in 1926, passed X in 1954, and finally rated PG in 1987. United States In the United States, the X rating was applied to a film that contained content judged unsuitable for children, such as extreme violence, strongly implied sex, and graphic language. When the MPAA film rating system began in North America on November 1, 1968, the X rating was given to a film by the Motion Picture Association of America (now the Motion Picture Association) if submitted to it, or due to its non-trademarked status, it could be self-applied to a film by a distributor that knew beforehand that its film contained content unsuitable for minors. From the late 1960s to about the mid-1980s, many mainstream films were released with an X rating, such as Midnight Cowboy, Medium Cool, The Girl on a Motorcycle, Last Summer, Last of the Mobile Hot Shots, Beyond the Valley of the Dolls, The Street Fighter, A Clockwork Orange, Sweet Sweetback's Baadasssss Song, Fritz the Cat, Flesh Gordon, Alice in Wonderland: An X-Rated Musical Comedy, Last Tango in Paris and The Evil Dead. Films that achieved critical and commercial success were later re-rated R after minor cuts, including Midnight Cowboy and A Clockwork Orange. The threat of an X rating also encouraged filmmakers to re-edit their films to achieve an R rating; one notable example of this was the 1987 action film RoboCop, which had to be edited eleven times before it could attain an R rating. Because the X rating was not trademarked, anybody could apply it to their films, including pornographers, as many began to do in the 1970s. As pornography began to become more popular and more legally and commercially tolerated, pornographers placed an X rating on their films to emphasize the adult content. Some even started using multiple X's (i.e. XX, XXX, etc.) to give the impression that their film contained more graphic sexual content