Thanks for your response, @Steve.
In regard to why I have found "Valid if” in “Validity” to be a little counterintuitive, I’m referring to using “Valid if” to create an enum or enunlist. It works but making such a list and checking for validity or user inputted data strike me as two different tasks. That’s why it struck me as counterintuitive to use the “Valid if” slot to make a list.
In regard to how an error can be produced, the main issue I’ve had to deal with is what happens after a value that has been recorded via “Valid if” to an enumlist column is no longer available in the enumlist due to changes that have occurred in the data. In such instances the app shows the user an “Invalid” error. I avoid this by making an action to erase the value that is no longer relevant and with produce an error but the combination or “enum maker” and “validity checker” functions had made the app building process for complicated for me.