Currency relative values of the different currencies. Currencies in this sense are defined by governments, and each type has limited boundaries of acceptance. Other definitions of the term "currency" are discussed in their respective synonymous articles banknote, coin, and money. The latter definition, pertaining to the currency systems of nations, is the topic of this article. Currencies can be classified into two monetary systems: fiat money and commodity money, depending on what guarantees the value (the economy at large vs. the government's physical metal reserves). Some currencies are legal tender in certain political jurisdictions. Others are simply traded for their economic
Shall and will The IETF (Internet Engineering Task Force) defines "shall" and "must" as synonymous terms denoting absolute requirements, and "should" as denoting a somewhat flexible requirement, in RFC documents. On specifications and standards published by the United States Department of Defense (DoD), requirements with "shall" are the mandatory requirements. (“Must” shall not be used to express mandatory provisions. Use the term “shall.”) “Will” declares intent or simple futurity, and “should” and “may” express nonmandatory provisions. Outside DoD, other parts of the U.S. government advise against using the word "shall" for three reasons: it lacks a single clear meaning, it causes litigation, and