 
   # Converts year, month, day to count of days since 0000-01-01.
   @doc false
-  @doc since: "1.5.0"
   def date_to_iso_days(0, 1, 1) do
     0
   end

  end

  @doc false
  @doc since: "1.5.0"
  def iso_days_to_unit({days, {parts, ppd}}, unit) do
    day_microseconds = days * @parts_per_day
    microseconds = div(parts * @parts_per_day, ppd)

    do: precision_for_unit(div(number, 10), precision + 1)

  @doc false
  def date_to_iso8601(year, month, day, format \\ :extended) do
    date_to_string(year, month, day, format)
  end
