 
       iex> Calendar.ISO.parse_utc_datetime("-2015-01-23T23:50:07,123+02:30")
       {:ok, {-2015, 1, 23, 21, 20, 7, {123000, 3}}, 9000}
+      iex> Calendar.ISO.parse_utc_datetime("+2015-01-23T23:50:07Z")
+      {:ok, {2015, 1, 23, 23, 50, 7, {0, 0}}, 0}
 
       iex> Calendar.ISO.parse_utc_datetime("2015-01-23P23:50:07")
       {:error, :invalid_format}

  @impl true
  def parse_date("-" <> string) when is_binary(string),
    do: parse_date(string, -1)

  def parse_date(string) when is_binary(string),
    do: parse_date(string, 1)

  def parse_naive_datetime("-" <> string) when is_binary(string),
    do: parse_naive_datetime(string, -1)

  def parse_naive_datetime("+" <> string) when is_binary(string),
    do: parse_naive_datetime(string, 1)

  def parse_naive_datetime(string) when is_binary(string),
    do: parse_naive_datetime(string, 1)

