I have a combo box with several choices in it including "other". I would
like to make it so that when the "other" option is selected, an input box
appears. When the user types in the details and presses enter, I want the
stuff they've typed to show as the selection in the combo box.

If that can't be done, then I'd like the input box to update a text box
below the combo box with the inputted data.

How to?