Canto Cumulus 8.5 introduced field validation via regular expression pattern matching. I've yet to do anything with it, but have been meaning too. We deal with ISBNs in our Cumulus catalogs and have always thought it was a prime target for validation. 
In the course of researching information for a different post, Google led me down the rabbit hole of links and found these little Gems: The first is the Wikipedia page for ISBNs where they break down each part of the number to show what it's used for and provide sample code for calculation. (hot!). The second is from Stackoverflow, discussing regular expressions for ISBN-13 and ISBN-10. 

I'm can't wait to try it out in my catalogs! Stay tuned for results...