MARC records differ from other bibliographic records in two important ways:
The primary way in which MARC records differ from non- MARC bibliographic records is in their reliance on numeric tags. Numeric tags typically consist of three digits followed by two spaces and two more digits. For example:
245 10 $a When you realize you have too many
kids: $b a guide / $c Hugh B
245 14 $a The angel with a dirty mouth /$c NickSteel ; illustrated by Melissa
The second way in which MARC tags differ from other bibliographic records is the use of subfields.
Each numerically tagged line in a MARC record may contain any number of subfields. A subfield typically consists of two consecutive characters, the first of which is the subfield delimiter which denotes the start of a new subfield. Examples of subfields are "$a" and "$x." The subfields do not have to be consecutive, as in the second record in the example above.
If you were creating a conventional filter for importing bibliographic records from a MARC database, you would have to anticipate a vast number of possible combinations, both of tags and of subfields.
Because it is difficult to anticipate every possible combination of tags and subfields in MARC records, EndNote provides you with a simplified way of creating filters for MARC records. The two sections that follow tell you how to create a filter specifically for MARC records, and then alert you to the different rules that EndNote uses when importing MARC records into an EndNote library.