Working with custom slips as introduced in Bug 32986, we want to put cover images for checked out items into the slip. Most cover providers allow retrieval by ISBN, but differ in whether they want ISBN-10 or ISBN-13. It'd be great to have a method to do this within a slip. It could be something within the slip generation code or within the biblioitems object. Either way, it'd be easier than putting a bunch of JS or TT into the slip.
Could we have a /Koha/Template/Plugin/ method to do this? Should probably do conversions both ways, ISBN13 to ISBN10 and ISBN10 to ISBN13. Note: Don't forget about 979* ISBNs.