date:parse-date() result mismatched format and date/time?

>From http://exslt.org/date/functions/parse-date/index.html:

	The first argument to date:parse-date is a string that gives a
	date/time in a particular format.

	The second argument is a string that gives the format pattern
	that has been used to format the date/time given as the first
	argument. The format pattern must be in the syntax specified by
	the JDK 1.1 SimpleDateFormat class.

But what should date:parse-date() return if the format given does not
actually match the date/time -- the empty string?

P.S.  If it's not too much trouble, please CC: replies to me as I'm not
subscribed to the list.

Thanks,
-- 
Kevin