How to validate text typed into text-input-range?

I am using a text-input-range and a text-input-choice in a popup-confirmer.

Dynamically enabling the OK button is possible using :change-callback in 
the text-input-choice. But I can type arbitrary non-numeric characters 
into the text-input-range without affecting the OK button since there is 
no :change-callback for that class. The :callback responds to arrow presses.

Text-input-range filters its input so that it is an integer, but it 
would be nicer if there was feedback about illegal characters.

Is there a way to make the OK button aware of unacceptable values typed 
into a text-input-range? Thank you.

Mitch