code: public static function compareCells(self $a, self $b)
      {
          if ($a->getRow() < $b->getRow()) {
              return -1;
          } elseif ($a->getRow() > $b->getRow()) {
              return 1;
          } elseif (Coordinate::columnIndexFromString($a->getColumn()) < Coordinate::columnIndexFromString($b->getColumn())) {
              return -1;
          }
  
          return 1;
      }
docs: Compare 2 cells.
  
  @param Cell $a Cell a
  @param Cell $b Cell b
  
  @return int Result of comparison (always -1 or 1, never zero!)