At all times, exactly one of the radio buttons in a set is checked.

Incidentally, some browsers actually follow spec on this. For example, if you're using Lynx, there's no way to vote for only some of the nodes on a page, unless you turn on your null vote setting. I have mine turned on for this reason -- not because I want to be able to change my mind, but because every once in a great while I get stuck in a Lynx-only scenerio for a few hours.

$;=sub{$/};@;=map{my($a,$b)=($_,$;);$;=sub{$a.$b->()}}
split//,".rekcah lreP rehtona tsuJ";$\=$ ;->();print$/
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