src/vs/workbench/contrib/notebook/browser/contrib/editorStatusBar/editorStatusBar.ts/ActiveCellStatus/_getSelectionsText
class ActiveCellStatus:	private _getSelectionsText(editor: INotebookEditor): string | undefined {
		if (!editor.hasModel()) {
			return undefined;
		}

		const activeCell = editor.getActiveCell();
		if (!activeCell) {
			return undefined;
		}

		const idxFocused = editor.getCellIndex(activeCell) + 1;
		const numSelected = editor.getSelections().reduce((prev, range) => prev + (range.end - range.start), 0);
		const totalCells = editor.getLength();
		return numSelected > 1 ?
			nls.localize('notebook.multiActiveCellIndicator', "Cell {0} ({1} selected)", idxFocused, numSelected) :
			nls.localize('notebook.singleActiveCellIndicator', "Cell {0} of {1}", idxFocused, totalCells);
	}