Using EXSLT to subtract dates

How can I use EXSLT extensions to subtract a date.

I see that there is a date-add开发者_如何学运维 function, but the EXSLT docs don't include any examples. I am trying to take the current date and subtract 1 month for example.

---

To subtract, add a negative durations.

See details in the XML Schema specification.

date:add($now, '-P1M')