... and this is when the development company (architect, technical director, ...) decides to extend the "data" models to the point where you've invented a programming language in XML. A programming language too advanced to use even for the programmers that invented it, let alone the "no code" people that it was intended for. A programming language with all of the complexities and none of the tooling that you would expect from a programming language, where failures are caught in runtime since you have no compile time checks of the XML that you throw at it.

Next step is, of course, to extend the XML validation to make sure it conforms to your application's expectations. And suddenly you have invented a compiler as well.