The date/time information is extracted from the header, shifted to the specified time zone, and the value of the given date-part is determined.
The test returns true if the resulting string matches any of the strings specified in the key-list.
The date test returns false if the specified header field does not exist, the field exists but does not contain a syntactically valid date-time specification, the date-time isn't valid according to the rules of the calendar system (e.g., January 32nd, February 29 in a non-leap year), or the resulting string fails to match any key-list value.
Unlike the header and address tests, the date test can only be applied to a single header field at a time. If multiple header fields with the same name are present, only the first field that is found is used.