Option to allow multiple expanded

I think there's value in providing an option to allow multiple/all accordions to be expanded, instead of forcing others closed when opening a new one.

The current behavior can be jarring when someone has a preceding (higher up) accordion expanded, then opens a lower one and the new accordion's top is scrolled well above the display so the user has to scroll up to read. This is because the one above collapsed, pulling the content up and out of view.