A pornographic film actor or actress, adult entertainer, or porn star is a person who performs sex acts in video that is usually characterized as a pornographic movie. Such videos tend to be made in a number of distinct pornographic subgenres and attempt to present a sexual fantasy and the actors selected for a particular role are primarily selected on their ability to create or fit that fantasy. Pornographic videos are characterized as either "softcore", which does not contain depictions of sexual penetration or "extreme fetishism" and "hardcore", which can contain depictions of penetration or extreme fetishism, or both. The genres and sexual intensity of videos is mainly determined by demand. Depending on the genre of the film, the on-screen appearance, age, and physical features of the main actors and their ability to create the sexual mood of the video is of critical importance. Most actors specialize in certain genres, such as gay sex, lesbian sex, bondage, strap-on sex, anal sex, double penetration, semen swallowing, teenage women, interracial or MILFs. The pornography industry in the United States was the first to develop its own movie star system, primarily for commercial reasons. In other countries, the "star" system is not common, with most actors being amateurs. Most performers use a pseudonym and strive to maintain off-screen anonymity. A number of pornographic actors and actresses have written autobiographies. It is very rare for pornographic actors and actresses to successfully cross over to the mainstream film industry. The number of pornographic film actors who have worked in the United States can be indicated by number of actors tested by Adult Industry Medical Health Care Foundation (AIM). When in 2011 its patient database was leaked it contained details of over 12,000 pornographic actors that it had tested since 1998. As of 2011, it was reported that roughly 1,200–1,500 performers were working in California's "Porn Valley".