I'm having trouble understanding the $i-m subfields in the Holdings
853-855 fields.  If I understand correctly, these subfields are used to
indicate how chronological data will be displayed on screen.  According
to the MARC manual, an entry in one of these subfields would be
something like (year), (week), etc.  Do I type in the parentheses?  How
come these are not control subfields like 853 $w?  Could someone please
give me some details or examples?

Thank you

Graham Barr <graham@DRA.COM>