ISO 8601 time classes
tu_week(x = integer(0))
yw <- linear_time(tu_week(1L), list(tu_year(1L)))
#> Error in linear_time(tu_week(1L), list(tu_year(1L))): could not find function "linear_time"
yw(Sys.Date())
#> Error in yw(Sys.Date()): could not find function "yw"