Message
iso-8601-date attribute "@iso-8601-date" if present must contain a valid date, date-time, time, or partial date in ISO-8601
format.
Rule XPath:
This rule ASSERTS the following, raising an alert if FALSE:
not(@iso-8601-date) or (@iso-8601-date castable as xs:dateTime) or (@iso-8601-date
castable as xs:date) or (@iso-8601-date castable as xs:gYearMonth) or (@iso-8601-date
castable as xs:gYear) or (@iso-8601-date castable as xs:gMonthDay) or (@iso-8601-date
castable as xs:gDay) or (@iso-8601-date castable as xs:gMonth) or (@iso-8601-date
castable as xs:time)