In comics, LGBT themes are a relatively new concept, as lesbian, gay, bisexual, and transgender (LGBT) themes and characters were historically omitted from the content of comic books and their comic strip predecessors due to anti-gay censorship. LGBT existence was included only via innuendo, subtext and inference. However the practice of hiding LGBT characters in the early part of the twentieth century evolved into open inclusion in the late twentieth and early twenty-first centuries, and comics explored the challenges of coming-out, societal discrimination, and personal and romantic relationships between gay characters. With any mention of homosexuality in mainstream United States comics forbidden by the Comics Code Authority (CCA) between 1954 and 1989, mainstream comics contained only subtle hints or subtext regarding an LGBT character's sexual orientation or gender identity. Starting in the early 1970s, however, LGBT themes were tackled in underground comix, independently published one-off comic books and series produced by gay creators that featured autobiographical storylines tackling political issues of interest to LGBT readers. The first openly gay characters in American comic strips appeared in prominent strips in the late 1970s and gained popularity through the 1980s. Since the 1990s, equal and open LGBT themes have become more common in mainstream US comics, including in a number of titles in which a gay character is the star. Today comic strips educating readers about LGBT-related issues are syndicated in LGBT-targeted print media and online in web comics. The popularity of comic books in Europe and Japan have seen distinct approaches to LGBT themes. A lack of censorship and greater acceptance of comics as a medium for adult entertainment in Europe has led European comics to be more inclusive from an earlier date, leading to less controversy about the representation of LGBT characters in their pages. Notable comics creators have produced work from France, Belgium, Spain, Germany and Britain. Japanese manga tradition has included genres of girls' comics that feature homosexual relationships since the 1970s, in the form of yaoi and yuri. These works are often extremely romantic and idealized, and include archetypal characters that often do not identify as gay or lesbian. Since the Japanese "gay boom" of the 1990s, a body of manga by queer creators aimed at LGBT customers has been established, including both bara manga for gay men and yuri aimed at lesbians, which often have more realistic and autobiographical themes. Pornographic manga also often includes sexualised