How to display messages next to fields in the site editor based on content of other fields

[nurkka]

Hi all!

I don't know where to start right now, so I would be grateful for any tips: I need to add a warning message to the first field of a RepeaterMatrix element, indicating when at least one specific other field within the RepeaterMatrix element contains a value. I think the task is not specific to Pro Fields, so I posted it here in general support.

Once this first message works, the second task would be to display a warning next to each of the combo field subfields, if the parent field contains a value.

In other words, I would need the ability to display warning messages next to fields in the page editor based on the value of other fields.

Does anyone know where to start implementing this?
Is it only possible with JavaScript or could there be any PW features to do it?