The latest release of our Open Platform Content API exposes for the first time the concept of 'references' on our tags and articles. Within our domain model, a 'reference' makes a link to either something in the 'real world', or to a specific piece of data in another system.
The ISBN-Tools module was born out of my need to be able to manipulate ISBN numbers for my own personal database of books. I just didn't want to have to trust my copying skills and I am certainly too lazy to hyphenate the numbers manually. Hence this library.