It would be great if we had the option to embed a warning in the default output value of transformers like the Attribute Value Mapper. It would work in a similar war to the “@Abort()” function, but instead of stopping the translation, it would return a custom warning in the log. This can be really useful in tools that are designed to be run by people who don’t know much FME and/or tools that are designed to run automatically.
As a side note, yes, I understand that you can just write a custom default value there and use it to identify the bad values downstream. This idea would essentially be an alternate way of doing that, and would be simpler/more direct.