Unobtrusive and Keyboard Accessible Connected Select Boxes
http://www.456bereastreet.com/archive/200704/unobtrusive_and_keyboard_accessible_connected_select_boxes/

Johansson, Roger
456 Berea Street
2007

Abstract:

Any web developer who has created a reasonably complex form is probably aware of the concept of multiple select elements that are connected – choosing something from one select box either makes a new select box appear or changes the options of one that is already visible.