Fixed Date

The fixed date holidays structure is a month-day pair based on a fixed date of either the Gregorian calendar or the Orthodox calendar.

Christmas Day

Orthodox Christmas

Weekday before/after Fixed Date

Some of the fixed date holidays are based on a given number of weekdays before or after a fixed date (making their calculated dates based on a fixed date, but not fixed).

Buß- und Bettag (Germany)

Based on a week number

Though week numbers are never used in worldwide public holidays, it is possible to construct a recurring holiday rule that is based on the weekday of a given week number, using the rule:

((7*(w-1))+(D-1)-3) days after the Thursday on or after January 1

where W is the week number and D is the weekday (running from 1-7 for Monday to Sunday). For more details, see the detailed example here.