Now it turns out that the client-side code related to this part of the product was still using fairly old support libraries. One of them, which was quite good in its time but is now outdated, is YUI.
So recently, as a maintenance step, we have replaced that code to use the modern Fetch API. This is now supported by all browsers except IE11, and for that browser we have what are called polyfills to keep things working. We have also rewritten the relevant code using Scala.js, which we use for all new client-side code. Things will be way more maintainable this way.
|Some of the new code using the Fetch API|
This change will be part of Orbeon Forms 2019.2.