Usually when documenting any type of program that you've created you want to consider the lowest common denominator for the people that will be using it. Course, what happens if you don't know your exact audience or it's so big that it includes everyone?
My guess is you have to document everything like this:
Compaq FAQ: Where do I find the "Any" key on my keyboard? (FAQ2859)
The term "any key" does not refer to a particular key on the keyboard. It simply means to strike any one of the keys on your keyboard or handheld screen.
I actually read this and was wondering if there actually was an "Any" key. Maybe I had just missed it all these years.