Accessibility is all about making a website accessible by as many people as possible - a lot of people tend to focus on blind users, as they suffer the majority of problems, but accessibility can benefit everyone: try using the accesskeys listed for a while, and see how much faster and easier the site can be..
Erin Arts Centre have an excellent article on why accessibility is important, but there's plenty more on the web if you do want to know more.
Your browser will allow you to access certain links using a keyboard combination. On Windows and Linux browsers, this is usually alt and the access key. On Mac browsers it is ctrl and the key. Internet Explorer for the PC will only select something when you press the access key. Hit return to activate the selected link or button.
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If you can think of more accesskeys that would be useful, please get in touch(7)