Removed this product specific information from Controlling focus with tabindex section. Cynthia thought maybe we need an FAQ on it:

This is necessary because authors supporting Internet Explorer must use keydown events to process keystrokes, where keydown but not keypress events are fired for non-alphanumeric keys. As web page authors implement script control over the keyboard they need to be able to use keydown but cancel the effect of consumed keystrokes such as arrow keys.