serif::dimensions::Frequency serif::dimensions::PhysicalQuantity dimensions.hpp std::string_view std::string_view serif::dimensions::Frequency::identifier identifier serif::dimensions::Frequency::identifier = "frequency" Dimension of Frequency. serif::dimensions::Frequency serif::dimensions::PhysicalQuantity serif::dimensions::Frequency identifier serif::dimensions::PhysicalQuantity std::basic_string_view< Char > std::string_view serif::dimensions::Frequencyidentifier