A proposal to allow any scroller to become the root scroller. Today's web endows the root element (i.e. the documentElement) with special powers (such as hiding the URL bar). This proposal would give authors more flexibility in structuring their apps by explaining where the documentElement's specialness comes from and allowing the author to assign it to an arbitrary scroller. See the explainer doc for a quick overview.
For up-to-date API usage information in the current experimental implementation in Chrome, see the user's guide.