[xsl] Computed dateTime

["Peter Flynn peter@xxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx>]

I need to do a number of calendar-based computations involving events 
determined by formulas such as "third Tuesday of the month" or "5th of 
the month provided it is not a Friday". It would be convenient to do 
them in the XSLT, although they could be done in a shell script 
pre-processor.

Before I go reinventing any wheels, is there a function I have missed 
like weekdayinMonth($date as gYearMonth)[1] to return the date of the 
first Sunday in the specified month and year?

Peter