Setting focus to text entry box in Storyline

This is a great thread, thanks everyone. I just wanted to add that I didn't need to create unique makser slides to get it to work. It's true you need the text box on the lowest layer, so any images that need to be behind the text box can't be on the slide timeline, but you can just put images in the slide background versus creating a new master slide for each slide. 

For example, I created 3 freeform text entry quiz slides all in a row, and I used the tab key as the submit. For each slide I used the black master slide. On each slide, I right-click the slide and select Format Background. Then change the fill to be a picture and use whatever background image you need as the background fill. With that method I'm able to tab to each slide and I see the blinking cursor on each slide AND they all have uniques background images. Cheers!