As part of the PRD item for creating public API for UI Controls for the sake of 3rd party Control authors, and as part of the requirement that we remove impl_ @treatasprivate API for an eventual JSR, we need to replace the private API we currently have for defining the backgrounds / borders of a Region with public API. We have several skins that are relying on these private internals, and should instead be using public API. This is the same API which is used by the CSS engine for styling the Region, and so we will also satisfy the request of several developers to have a way to modify the visuals of a UI control (at least in part) from Code without CSS by exposing this API.