Hello! I want to make a form in which one of the fields is filled with a list of two numbers (a 2D coordinate) via a ClickPane or LocatorPane. Is it possible? I cannot figure it out! It seems from the documentation that I should be able to specify something like a ClickPane as an arbitrary function, but the first problem is that I can't see how to make an arbitrary function return a value to the form. For example, here is an even simpler example using a slider. This works:

form = FormFunction[
   FormObject[{"Number" -> <|"Interpreter" -> "Real", 
       "Control" -> Slider|>}], Print];
form[]

But this doesn't:

form = FormFunction[
   FormObject[{"Number" -> <|"Interpreter" -> "Real", 
       "Control" -> Function[Slider[0, {0, 1}]]|>}], Print];
form[]

The value returned is always 0.

Can anyone show whether it is possible to make custom function that fills a form field?