> the first Tuesday in
> Novemeber or [...]
> the 3rd Monday in Feb.
If you are interested in such issues, you could read chapter 4.11 in "XSLT
cookbook" second edition (dec 2005) where relevant code is provided.
According to the author, Sal Mangano, such dates are "easy to handle"
(p. 155). With this book as an inspiration, "last" could be specified with
an HYPHEN-MINUS (U+0x2D).