def updated_from index
      index.upto(@rows.size - 1) do |idx|
        row = row(idx)
        row.idx = idx
        row_updated idx, row
      end
    end
def updated_from index
      index.upto(@rows.size - 1) do |idx|
        row = row(idx)
        row.idx = idx
        row_updated idx, row
      end
    end
Renumbers all Rows starting at _idx_ and calls #row_updated for each of
 them.