These and kindred questions need discussion, and need it urgently, in the few years left to us before somebody presses the button and the rockets begin to fly.

Another way is to have a button that adds new keyword fields on the fly to allow users to add as many keywords as they want.

The DHTML object model lets you modify on the fly the structure of the page, but all the changes will be lost as soon as you refresh the view by hitting F5 or clicking the browser's refresh button.