firstDay

Change which day of the week is first on the calendar.

DateTime 1.0.0 This value represents which day of the week should be in the first column of datetime. If `null` is given autodetection will be attempted, and if that fails, 1 (Monday) will be used. The days are 0 indexed starting from Sunday: * 0 - Sunday * 1 - Monday * 2 - Tuesday * 3 - Wednesday * 4 - Thursday * 5 - Friday * 6 - Saturday The default value of `null` will result in auto detection being used. This option allows for the "first" day to be changed to any of the days of the week as desired. As of DateTime 2, this parameter supports auto detection through the browser's native [`Intl.Locale` API](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/Locale). Please note that this API isn't supported in Firefox at the time of writing. If the auto detection fails, `1` (Monday) will be used.