I don't see `block.cover` documented http://developer.thegrid.io/api.html#content-management-item Is there a key for faces + saliency bbox, or do I need to derive that? @automata I need to decide where/how to save user-defined focus rectangle - `block.metadata.coverPrefs.scene` -- ok? - `{x,y,width,height}` -- top-left, bottom-right points of original pixels ok?