The numbers to the left and right of the syyyy are 2 different DayValues whose years are to be compared.
➢Note that you can replace yyyy by any of the YYyy, yyYY and YYYY combinations, and these rules will be "added" to those below.
A common use of this token is in weekly diaries, where the begin/end dates of the weeks are displayed differently if the week straddles a month boundary.
Using the following tokens :
[1Mmm] [1d] [1syyyy7] to [7Mmm] [7d] [7yyyy]
[8Mmm] [8d] [8syyyy14] to [14Mmm] [14d] [14yyyy]
allows you to show the year of the first day of the week, only if the year changes during the week.
Dec 6 to Dec 12 1999
Dec 27 1999 to Jan 2 2000
Use filler tokens suffixes if the current token is next to a separator such as "-" or "/" and you do not want that separator to appear when the conversion of the comparative year token is blank.
See also: [MonthHeader] change of month/year tokens.