This method determines the month and year displayed on opening. The default setting is the current month and year, taken from the operating system.
If the display option flag GTK_CALENDAR_NO_MONTH_CHANGE is set, the user will be unable to switch from the month and year passed as parameters.
Note that the month must be in the range 0 to 11, similar to PHP's date('m'). The year is in 4-digit format, as in 2002 the format returned by date('Y').