The code must always be clearly legible in the publication (minimum font size 9).
For printed material, the identifier is marked:
ISMN 979-0-321-76543-1 (score)
ISMN 979-0-321-76544-9 (piano score)
ISMN 979-0-321-76545-7 (set of parts)
If a book or notated music publication is available electronically, all of its product forms (e.g., CD-ROM or file formats such as PDF, EPUB, etc.) are assigned separate ISBN or ISMN identifiers, as they must be identifiable as separate products in the supply chain.
Section 6 of the ISBN Users’ Manual features more information on identifying electronic material and DRM protection.
Typically, a multi-volume publication will only be assigned one ISBN identifier. In addition, each volume will be assigned its own ISBN.