MARC 21 Format for Bibliographic Data is designed to be a carrier for bibliographic information about printed and manuscript textual materials, computer files, maps, music, continuing resources, visual materials, and mixed materials. Bibliographic data commonly includes titles, names, subjects, notes, publication data, and information about the physical description of an item.The bibliographic format contains data elements for the following types of material:Books (BK) - used for printed, electronic, manuscript, and microform textual material that is monographic in nature.Continuing resources (CR) - used for printed, electronic, manuscript, and microform textual material that is issued in parts with a recurring pattern of publication (e.g., periodicals, newspapers, yearbooks). (NOTE: Prior to 2002, Continuing resources (CR) were referred to as Serials (SE)).Computer files (CF) - used for computer software, numeric data, computer-oriented multimedia, online systems or services. Other classes of electronic resources are coded for their most significant aspect. Material may be monographic or serial in nature.Maps (MP) - used for all types of printed, electronic, manuscript, and microform cartographic materials, including atlases, sheet maps, and globes. Material may be monographic or serial in nature.Music (MU) - used for printed, electronic, manuscript, and microform music, as well as musical sound recordings, and non-musical sound recordings. Material may be monographic or serial in nature. Visual materials (VM) - used for projected media, non-projected media, two-dimensional graphics, three-dimensional artifacts or naturally occurring objects, and kits. Material may be monographic or serial in nature.Mixed materials (MX) - used primarily for archival and manuscript collections of a mixture of forms of material. Material may be monographic or serial in nature. (NOTE: Prior to 1994, Mixed materials (MX) were referred to as Archival and manuscript material (AM)).