Google implies that this is a page of gmail keyboard shortcuts
http://mail.google.com/support/bin/answer.py?hl=en&ctx=mail&answer=6594
which you reach by pressing the question mark, ?, in gmail, and then selecting "Open in a new window" is the same
as the black pop-up window below. Maybe that is the intent, but the content is rapidly drifting apart. :-(
Scroll across using scroll-bar below image: