I have a Web App (Web AppBuilder Dev Edition) that has the Smart Editor widget enabled on a Feature Service that is published with a Relationship Class on a Table.
Smart Editor is great because it enables the user to edit the geometry feature service and also the related table.
Since I am using Developer Edition, I have access to the underlying files that drive the web app. I'm looking for the location of the text string "Related Table/Layer" in the files. I would expect it to be in an HTML file somewhere, but my searching in the files comes up short.