namespace std::chrono {
class weekday {
unsigned char wd_; // exposition only
public:
weekday() = default;
constexpr explicit weekday(unsigned wd) noexcept;
constexpr weekday(const sys_days& dp) noexcept;
constexpr explicit weekday(const local_days& dp) noexcept;
constexpr weekday& operator++() noexcept;
constexpr weekday operator++(int) noexcept;
constexpr weekday& operator--() noexcept;
constexpr weekday operator--(int) noexcept;
constexpr weekday& operator+=(const days& d) noexcept;
constexpr weekday& operator-=(const days& d) noexcept;
constexpr unsigned c_encoding() const noexcept;
constexpr unsigned iso_encoding() const noexcept;
constexpr bool ok() const noexcept;
constexpr weekday_indexed operator[](unsigned index) const noexcept;
constexpr weekday_last operator[](last_spec) const noexcept;
};
}

weekday represents a day of the week in the civil calendar.

It normally holds values in the range 0 to 6,
corresponding to Sunday through Saturday, but
it may hold non-negative values outside this range.

It can be constructed with any unsigned value,
which will be subsequently truncated to fit into weekday's unspecified internal storage.