International Standard Book Number, the international code for identifying a particular version or printing of a book
Within the ISBN, spacing, hyphens, and punctuation should be preserved.
Inside the book metadata (<book-meta>), successive <isbn> elements may be used to records as many ISBNs for the book as necessary. Some multi-volume works have ISBNs assigned to the series as well as to the individual volume and both may be recorded. Best practice is to delete the word “ISBN”, although some archives have chosen to retain it.
The @content-type attribute used to differentiate between ISBNs or explain the reason for a particular ISBN.
ISBNs can be assigned to books, reports, standards documents, conference proceedings, dissertations, and some serial publications. The <isbn> element can also be used to record all such numbers inside bibliographic citations (<element-citation> and <mixed-citation>). Within a mixed-style citation, the text “ISBN:”, if present, should be kept as text within the citation but not placed inside the <isbn> element. Within an element-style citation, the text “ISBN:”, if present, should be removed from the citation and also not placed inside the <isbn> element.
<!ELEMENT isbn (#PCDATA %isbn-elements;)* >
Text, numbers, or special characters, zero or more
... <book-meta> ... <book-title-group> <book-title>Wildflowers of the Washington Area </book-title> </book-title-group> <contrib-group> <contrib contrib-type="author"> <name><surname>Lapeyre</surname> <given-names>Deborah A.</given-names></name> </contrib> <contrib contrib-type="author"> <name><surname>Usdin</surname> <given-names>B. Tommie</given-names></name> </contrib> </contrib-group> <publisher> <publisher-name>Lippman, Ltd.</publisher-name> <publisher-loc>Bethesda, MD</publisher-loc> </publisher> <isbn>0-23-8675-309</isbn> <pub-date><year>2002</year></pub-date> ... </book-meta> ...