Requiring text in text entry box

I've spent half of my afternoon scouring the internet to figure out how to do this, with no luck so far...

I need to have a text entry box where the user is required to enter text before they can click the "submit" button.  Initially I tried to do this with a short answer question slide, where I could simply employ the "incomplete" caption, but the text entry needs to be multiple-line, and scrolling if necessary.  Short answer slides are not the answer.

For a default text entry box, the "submit" button is clickable even if the box is empty. How do I (and is it even possilbe) set up a TEB requirement for something (anything) to be entered before the "submit" button is accessible?

Thank you!!