865 template <typename Derived> struct null_chrono_spec_handler {  struct
866   FMT_CONSTEXPR void unsupported() {  in unsupported()
869   FMT_CONSTEXPR void on_year(numeric_system, pad_type) { unsupported(); }  in on_year()
870   FMT_CONSTEXPR void on_short_year(numeric_system) { unsupported(); }  in on_short_year()
871   FMT_CONSTEXPR void on_offset_year() { unsupported(); }  in on_offset_year()
872   FMT_CONSTEXPR void on_century(numeric_system) { unsupported(); }  in on_century()
873   FMT_CONSTEXPR void on_iso_week_based_year() { unsupported(); }  in on_iso_week_based_year()
874   FMT_CONSTEXPR void on_iso_week_based_short_year() { unsupported(); }  in on_iso_week_based_short_year()
875   FMT_CONSTEXPR void on_abbr_weekday() { unsupported(); }  in on_abbr_weekday()
876   FMT_CONSTEXPR void on_full_weekday() { unsupported(); }  in on_full_weekday()
877   FMT_CONSTEXPR void on_dec0_weekday(numeric_system) { unsupported(); }  in on_dec0_weekday()
878   FMT_CONSTEXPR void on_dec1_weekday(numeric_system) { unsupported(); }  in on_dec1_weekday()
879   FMT_CONSTEXPR void on_abbr_month() { unsupported(); }  in on_abbr_month()
880   FMT_CONSTEXPR void on_full_month() { unsupported(); }  in on_full_month()
881   FMT_CONSTEXPR void on_dec_month(numeric_system, pad_type) { unsupported(); }  in on_dec_month()
882   FMT_CONSTEXPR void on_dec0_week_of_year(numeric_system, pad_type) {  in on_dec0_week_of_year()
885   FMT_CONSTEXPR void on_dec1_week_of_year(numeric_system, pad_type) {  in on_dec1_week_of_year()
888   FMT_CONSTEXPR void on_iso_week_of_year(numeric_system, pad_type) {  in on_iso_week_of_year()
914 struct tm_format_checker : null_chrono_spec_handler<tm_format_checker> {  argument