Most fields contain several related pieces of data. Each type of data within the
field is called a subfield, and each subfield is preceded by a subfield code. Subfield codes are one lowercase letter (occasionally a number) preceded by a delimiter.
A delimiter is a character used to separate subfields. Each subfield code
indicates what type of data follows it.
In the following example, the field for a book's publication information is defined by the tag 260. This field includes 3 subfields with subfield codes "a", "b", "c".
260 New York : ‡b Meridian, ‡c c1976.
Subfield "a" is for the publisher's location (New York). The symbol "‡a" usually does not show. The subfield "b" is for the publisher (Meridian), and subfield "c" is for the publication or copyright date--c1976.
