Convention on Copyright. Copyright is a related concept, but pertains to Anglo-American common law; one notable difference is that copyright does not generally involve moral rights. The legal clauses governing authors' rights and related rights form the first book of the French Code of Intellectual Property (CPI). This article will thus refer to articles from this code as CPI Lnnn. The notion of 'author' extends to that of composer (of music), playwright, painter, photographer, etc., though the law makes it a requirement that the work should be original (or show some supplemental originality, in the case of a derived work) in order to be protected. In practice authors often cede their rights to publishers, who then enforce the "exclusive right" and some are members of societies that enforce their rights on their behalf. The latter is de facto nearly compulsory in case of songwriters and composers, almost all of whom are members of Sacem. Performers and publishers of audio recordings enjoy "related rights". These follow different rules and have a shorter duration than the rights of authors. In practice performers often cede their rights to publishers, or have them enforced by societies. The exclusive right of the author is not absolute. According to WIPO treaties, local legislation may make exceptions to exclusive copyrights only if these exceptions fulfill a "three-step test": limitations and exceptions should only concern special cases; should not conflict with a normal exploitation of the work; should not unreasonably prejudice the legitimate interests of the right holder. This is how the US doctrine of fair use is justified with respect to copyright treaties for instance. The 2001 European Directive on Copyright proposes a list of 10 exceptions to copyright that member states can choose to implement or not, in addition to one whose implementation is compulsory (this makes an exception for temporary technical copies, meant to address Web caches and similar systems). Exceptions to copyright in French law are defined in CPI L122-5. Among them is the notable exception for private copies: French residents may freely make copies of works (except software) for their private use, and freely display those works within their family circle (which is interpreted to include friends), without the agreement of the copyright holder. However, French law includes a "tax on private copies" meant to address the losses incurred by copyright holders; this tax is levied on blank media (audio and video cassettes,