[development] combo box

Hi. I have a new site to do, and (so far) there are 3 things I haven't done before in Drupal. I'll make each a different message so the thread doesn't get confused. The first one is what is/used-to-be? called a combo box. That is, a select box that also allows one to type in an entry if none of the options will do. In terms of the operation of a normal combo, the issue is that while I can put a text box above a select, and when submitted, take the selected option, if one, or the text box contents, if any, normally a combo will take an option selection and deposit that text in the text-box portion, in case you want to edit it.