Creates a date value. The format is quite flexible, the main issue is avoid ambiguous dates. Dates like 4/8/2000 could be interpreted as 4th August or 8th April. This issue can be avoided in several ways: you can use the ISO format (e.g. date{2010-04-05} is 5th April), or you can use an (English) month name, e.g. date{5 April 2010}