Stefan Koopmanschap had a problem - the formatting on his dateTime fields (the XSD type) wasn't cooperating and couldn't be validated. He asked the question of the community of how to correct this and was given a short and easy answer from David Zuelke using date.
Recently I had to compose some XML documents that needed to be validated with XSDs. All fine of course, but I had some problem with two date/time fields that according to the XSD were supposed to be xs:dateTime fields. Googling around I found a lot of references to the ISO8601 format, so I decided to format my date using the DATE_ISO8601 constant. That did not work though.
David's suggestion was to use "date('c')" (the full ISO 8601 date) instead of the DATE_ISO8601 constant. The trouble is caused by a missing colon in the second choice's output.