Question

Several radio buttons with the same name act as a set, where checking one unchecks the others.
What is the scope of this behavior?

1. The form in which the button resides
2. The page / document on which the button resides
3. Does scope pass into iframes?

I have always used them in forms, but now writing formless HTML (using ajax for posting), and everything seems to be working just fine, so my guess is #2.

Answer 1

Radio buttons with the same name in the same form act as a set, but not with those of different forms. Radio buttons with no form act as a set with those with no forms.

test it yourself:
http://jsfiddle.net/8qqNC/1/