The Offset recurrence options lets you specify if a certain number of days or weekdays.should be added to the rule specified by the type and weekdays recurrence options. This is useful in cases when holidays follow each other and the first holidays has some complex behaviour (usually due to a specific behaviour when it occurs on a weekend), or for holidays that last more than 1 day but which have a different name on each day (for example Hannukah).
For example, in some English speaking countries, Christmas (as a legal holiday) is celebrated on December 25 but is moved to Monday if it falls on Saturday or Sunday, giving the following :
In the same context, Boxing Day is defined as the day after Christmas. A simplistic setting of its rule as December 26 (move weekends to Monday) would give the following :
which is clearly incorrect in 2004 and 2005, since it gives the same date for both Christmas and Boxing Day.
Using the rule December 25 (move weekends to Monday) with the setting add 1 day to the above rule, gives the following which is correct (except for the UK).
The option Add/subtract X days/weekdays to/from above rule is also useful fo multi-day holidays such as Chinese New Year or Ramadan (and other Muslim feasts) where the name of the 2nd and 3rd days of the holiday may need to be displayed differently from the first day, thus preventing the use of the duration option.
Important: the Weekdays part of a recurrence rule is processed before the present Offset options.