The basic divisions of the MARC 21 bibliographic are:
In discussions of MARC 21 tags, the notation XX is often used to refer to a group of related tags. For example, 1XX refers to all of the tags in the 100s: 100, 110, 130, and so on.
|0XX||Control information, numbers, codes|
|1XX||Main Entry (e.g. Author, etc.)|
|3XX||Physical description, etc.|
|6XX||Subject added entries|
|8XX||Series added entries|
|9XX||Locally defined uses (NOTE: all Evergreen records have a 901 tag. Do not delete this tag.)|