Auto fill content fields when saving a content

Hello,

I have the next requirement and I not finding any clean way in the documentation to implement it.

Basically, we need a new field © which value must be filled with the content of another two fields (A and B) under the criteria of taking A if is not empty or B otherwise.
The field C will be hidden so the editor can’t tamper with it.

There is something similar to a custom interceptor class that would allow me to change the value after the customer save the content?

So far, I think I could use a custom validator or using javascript but I don’t know yet if are viable.

Thanks for your help in advance

This sounds like a job for:

To not show the field just make sure it isn’t referenced in the namespace editor:templates definition.

Thanks! we are going to give it a try right now.