PLEASE BE WARNED – use this class only for dates after 1582 AD; that's the beginning of the epoch. Dates before 1582 will not be correctly printed. In addition, since ten days were lost from October 5 through October 15, operations between a Gregorian date (after 15-Oct-1582) and a Julian date (before 5-Oct-1582) will give incorrect results; or, 4-Oct-1582 + 2 days will yield 6-Oct-1582 (a non-existent day!), not 16-Oct-1582.
In fact, if you pass a year < 1582 to a method like #newDay:month:year: it will assume that it is a two-digit year (e.g. 90=1990, 1000=2900). The only way to create Julian calendar dates is with the #fromDays: instance creation method.