In some languages, a month name that is part of a date appears in the genitive case. For example, a date in the ru-RU or Russian (Russia) culture consists of the day number and the genitive month name, such as 1 Января (1 January). For these cultures, if a custom format string includes the "MMM" format specifier, the DateTime.ToString or DateTimeOffset.ToString method includes the appropriate member of the DateTimeFormatInfo.AbbreviatedMonthGenitiveNames array in place of the "MMM" in the result string.

In a set operation, the array must be one-dimensional with exactly 13 elements, because System.Globalization.Calendar objects accommodate calendars that have 13 months. For calendars that have 12 months, the thirteenth element should be string.Empty.

If you set the DateTimeFormatInfo.AbbreviatedMonthGenitiveNames property, you must also set the DateTimeFormatInfo.AbbreviatedMonthNames property.