ICellRegion satisfies this structurally, so every existing caller (a Contentful partition's
members) needs no change. It also lets a bare ICellRange profile itself — renderCellRange
adapts one with a four-line object, getRange returning the range itself — without a region ever
having been asked for.
What profileRegion needs to read — the anchor cell and the extent, nothing a partition knows that a plain range does not.