29 Time library [time]

29.8 The civil calendar [time.cal]

29.8.2 Class last_spec [time.cal.last]

namespace std::chrono { struct last_spec { explicit last_spec() = default; }; }
The type last_spec is used in conjunction with other calendar types to specify the last in a sequence.
For example, depending on context, it can represent the last day of a month, or the last day of the week of a month.