User:Rich Farmbrough/ISBN/Template:Auto isbn/doc

undefined is called this way,

a. Suppose we have a 10 digit ISBN 0-593-01518-5

b. Suppose we have a 13 digit ISBN 978-0-593-01518-6

Up to 1 January 2007 this will display

ISBN

Afterwards as

ISBN

Clearly this would be tedious and error prone to do by hand so most uses of the template are expected to be set up by automated or semi-automated processes.