A contribution spec as a registration: the one mapping for a saved row, the placement preview
and the artifact viewer's preview. Ranked 0 and keyed only by the spec's own key; a caller that
knows more (a row's precedence, a preview's derived key) sets it on the result.
A contribution spec as a registration: the one mapping for a saved row, the placement preview and the artifact viewer's preview. Ranked 0 and keyed only by the spec's own key; a caller that knows more (a row's precedence, a preview's derived key) sets it on the result.