The currency of the price, or a price component when attached to [[PriceSpecification]] and its subtypes.\n\nUse standard formats: [ISO 4217 currency format](http://en.wikipedia.org/wiki/ISO_4217) e.g. "USD"; [Ticker symbol](https://en.wikipedia.org/wiki/List_of_cryptocurrencies) for cryptocurrencies e.g. "BTC"; well known names for [Local Exchange Tradings Systems](https://en.wikipedia.org/wiki/Local_exchange_trading_system) (LETS) and other currency types e.g. "Ithaca HOUR".