Style guide: radio button

* Definition says "Assumption is that one will always be selected". I'm 
not sure this is always true. I just filled out something the other day 
with multiple radio groups per page, where each radio group starts out 
unfilled. It was useful because you can see what you have filled out or 
not. If you tab into the radio group, nothing is selected until you hit 
space or arrow.
* A very important use case is embedded fields in a radio item (this also 
happens a lot with checkboxes). For example in the standard Windows print 
dialog, it has:
( ) All
( ) Pages from ____ to ____
( ) Selection

It's important to say how to label these things, as well as how it affects 
arrow or tab navigation

- Aaron