The American Library Association maintains a list of the most challenged books, which are frequently claimed to be inappropriate for children. They stated in a release by the National Coalition Against Censorship that "This year's #1 banned book, Captain Underpants... is the gift that keeps on giving. Because these popular, silly books are read by parents, with their children, all over the country. The potty humor makes parents roll their eyes and kids giggle. The absurdity of banning books in order to attack perceived moral problems is exemplified by this year's winner. Both the MPAA film rating system and most television content rating systems have ratings for family-friendliness: a G rating in either is universally acceptable for all audiences, while a PG rating suggests that, while generally safe for children to watch, that there should be a parent or guardian present for guidance, since some mild adult-oriented material may be present. The MPAA's film rating system has not been without controversy (itself established after the Hays Code, which required all films to be at least somewhat family-friendly, was abolished), as theater chain interest groups have noted that films rated as high as R (adult-oriented films that persons under 17 cannot watch without an adult) could be interpreted as being family-friendly if the viewer is tolerant of profanity, while others may have far too much graphic violence or borderline-pornographic sexual images to be suitable for children. An overwhelming theme of television in the 1980s and 1990s was the trend of the family sitcom. Family sitcoms had also been popular during the 1950s and 1960s as well with shows such as "Father Knows Best", "The Adventures of Ozzie and Harriet", "Leave It To Beaver", and "Gidget". This trend became again enormously popular in the 1980s and 1990s with shows such as "Full House", "Boy Meets World", "Growing Pains", "Family Ties", "Family Matters", "Home Improvement", "The Fresh Prince of Bel-Air", "Blossom" and "Step by Step". During their prime, these shows were some of the hottest sitcoms on TV. The North American Entertainment Software Rating Board, which rates video games, classifies family-friendly content with an E rating. A family-friendly (or all-ages) show, event or venue refers to one with no age restrictions for entry. In the United States, as applied to the world of concerts, this can refer to a show or venue where minors are permitted to attend a live performance, since those who are not of legal drinking age are generally not permitted in bars, but are permitted in restaurants which serve alcoholic beverages.