I've noticed while using the Standard Selection tool, once I have an area selected I can move the selection marquee around by using the arrow keys on my keyboard. The longer I hold an arrow key down, the faster it goes.
Yet, I can find nothing in the documentation regarding this functionality. That doesn't mean it isn't documented - it just means I couldn't find it.
Are there other undocumented (or otherwise) keyboard commands that control the selection marquee?