I’ve been working on a few CKEditor plugins recently for some projects. When building the elements of a dialog you create a data structure like:

This is great, but what if you want multiple validation criteria for example it must be a number and not empty? There are a handful of hacks and examples of this online, but looking through the code I found an undocumented (and otherwise unused) function which enables you to combine multiple validation functions:

You can pass as many validation functions into this as you want and it will combine them, but only allows you to specify one validation message unfortunately.