# File lib/ri_cal/property_value/date_time/time_machine.rb, line 124
        def at_start_of_iso_year(wkst)
          start_of_year = @date_time_value.iso_year_start(wkst)
          change(:year => start_of_year.year, :month => start_of_year.month, :day => start_of_year.day)
        end