Date , which can be the publication or access date, and date parts , for formatting day, month, year or date ranges.
Names , for formatting names of authors, editors, publishers.
Number , for formatting numeric variables, such as issue or volume numbers.
Label , to format certain types of data ("vol." or "volume", for example).
Group , to specify delimiters or formatting for a group of elements. Particularly useful to avoid this kind of thing: New York, NY: , 1990, which can occur when one element is missing in the reference (in this case the publisher).