Expanding text field?

I want to type into a text field and have the field expand as I type.
When I set the 'expand to fit' option, the text field stays the same size as I type and scrolls inside the field, but then resizes to accommodate all the text I've typed after I hit Enter.

(I've got my form saved as dynamic).

I've read lots of the forums here and still don't know if 'expandable' text field refers to the field expanding as I type, or expanding after I've typed in everything.

Can someone help me out pls?

Thanks.