applications since the enactment of the Patent Act of 1836. However, even among patent legal systems in which the claims are used as the reference to decide the scope of protection conferred by a patent, the way the claims are used may vary substantially. Traditionally, two types of claiming systems exist: the "central claiming system", according to which the claims identify the "centre" of the patented invention. The exact scope of the protection depends on the actual nature of the inventor’s contribution to the art in the concerned technology. the "peripheral claiming system", according to which the claims identify the exact periphery, or boundary, of the conferred protection. In this system, the burden of drafting good claims is much higher on the patent applicant (or on his or her counsel). The applicant receives the protection he or she requested and almost nothing more, provided that the invention is new and non-obvious. This theoretically makes it easier for third parties to examine whether infringement may exist or not. No patent system today is a purely either central or peripheral, but the system used in Germany and most of the other countries of continental Europe is considered more central than the system currently used in the United Kingdom, the United States, and especially Japan, which are more peripheral. In recent years, Japan's system has become more peripheral, while the system used in the United States was becoming more central because of the increasing resort in US patent litigation to the doctrine of equivalents to expand claim scope unpredictably, until the US Supreme Court reversed that trend in the Warner-Jenkinson case in 1997. Requirements and structure In most modern patent laws, patent applications must have at least one claim, which are critical defining elements of the patent and the primary subject of examination. In some patent laws however, a date of filing may be obtained for an application which does not contain any claim. European Patent Convention Under the European Patent Convention (EPC), a claim must define the matter for which the protection is sought in terms of technical features. These technical features can be either structural (e.g. a nail, a rivet) or functional (e.g. fastening means). Regarding the structure of a claim, under the EPC, what is called the "preamble" is different from the meaning the "preamble" has under U.S. patent law. In an independent claim in Europe, the preamble is everything