Rosh Hashanah
The first two days of the Ten Days of Repentance are on Rosh Hashanah. One of those days may occur on a Shabbat as well, making that day of Rosh Hashanah on which Shabbat occurs stricter in observance, meaning the observances of Shabbat are followed than a Rosh Hashanah that occurs on any other day but Shabbat (Saturday). When Rosh Hashanah occurs on a Shabbat a few additional prayers in the mahzor ("prayer book") are added as well as excluded in keeping with the combined theme of a Rosh Hashanah and Shabbat combination.