The issues regarding copyrighted works on the Internet are widely debated and laws continue to grow and change in response to the ever changing nature of the Internet Copyrights are generally assumed for any original creative works made after April 1, 1989, according to the Berne copyright convention, though what constitutes fair use of copyrighted material on the Internet remains in many cases unclear. Certain Internet copyrights, such as Creative Commons copyright licenses, allow for more freedom regarding the use of copyrighted works. Certain licenses may allow derivative works with proper attribution. The popularity of what is called "fan fiction" on the Internet has been the topic of much discussion regarding copyright laws. Works of fan fiction, where writers post original stories on the Internet featuring characters from other copyrighted works, such as Star Trek, are derivative works, causing a great deal of fan fiction to be in violation of copyright laws. A gray area exists, however, because parody is covered under fair use laws, and it can often be hard to distinguish derivative fan fiction from fair use parody. Due to this, many copyright holders choose to turn a blind eye to the large amounts of fan fiction available on the Internet.