Mastering Regular Expressions Jeffrey E.F. Friedl Nutshell Handbook Series O'Reilly & Associates, Inc. 1997 ISBN 1-56592-257-3
See the software section
International Standard Book Number = 10-digit or 13-digit codes used by the publishing industry to uniquely identify individual book titles and editions. Some 10-digit ISBNs may end with an "X" instead of a digit.