This is a list of ISBN identifier groups, the second element in 13-digit ISBNs (the first element in 10-digit ISBNs). The identifier is assigned to mark either a publisher's place of business or the language of the books it publishes. The "original" set of identifiers, assigned prior to the introduction of 13-digit ISBNs and, as such, prior to 978-prefix books, ranged from one to five numerical digits, according to the following structure: They are assigned in approximate descending order of publishing volume. Because the smaller identifiers have room for fewer publishers and ISBNs, several countries have had more than one identifier assigned to them. On the other hand, several countries (Australia, Canada, France, Austria, Switzerland...) have no identifier because they fall in the "language groups". The structure for the identifiers of the 979- prefix and whether it will have language-specific identifiers is not well known, but four identifiers have been assigned (979-10, to France, 979-11, to the Republic of Korea, 979-12, to Italy, and 979-8, to the United States of America). Also, 979-0 has been reserved for the use of International Standard Music Number for sheet music. A 977- prefix indicates International Standard Serial Numbers.