none as default action for keyup event is not consistent with reality

[Zhang-Junzhi]

The spec says in many places that keydown may have associated activation behaviors while explicitly saying the default action of keyup is none ([1], [2], [3]).

However, this is not true in reality. In most OSs/UAs, [Space] keyup, instead of [Space] keydown, triggers click for <button> elements. I think the spec may need to be updated to be consistent with reality.