Hi all, I propose to change the specification to remove any elements that are no longer associated with the form from the past names map: http://www.whatwg.org/specs/web-apps/current-work/multipage/forms.html#past-names-map
It's strange for elements to linger around forever in the past names map after the element get associated with a new form element. Since IE didn't support form attribute for a long time (or maybe still hasn't?), I don't think there is any compatibility concern. The change makes the elements associated with the form element more consistent and easier to reason about. We can make form[x].form === form an invariant for every x such that form[x] is a form control element. - R. Niwa
