namespace std::chrono {
  class month_weekday {
    chrono::month           m_;         
    chrono::weekday_indexed wdi_;       
  public:
    constexpr month_weekday(const chrono::month& m, const chrono::weekday_indexed& wdi) noexcept;
    constexpr chrono::month           month()           const noexcept;
    constexpr chrono::weekday_indexed weekday_indexed() const noexcept;
    constexpr bool ok() const noexcept;
  };
}
month_weekday represents the 
nth weekday of a month,
of an as yet unspecified year
.  To do this the 
month_weekday stores a 
month and a 
weekday_indexed.[
Example 1: 
constexpr auto mwd
    = February/Tuesday[3];              
static_assert(mwd.month() == February);
static_assert(mwd.weekday_indexed() == Tuesday[3]);
 — 
end example]
month_weekday is a trivially copyable and standard-layout class type
.