code: public static function getRangeBoundaries($pRange)
      {
          // Ensure $pRange is a valid range
          if (empty($pRange)) {
              $pRange = self::DEFAULT_RANGE;
          }
  
          // Uppercase coordinate
          $pRange = strtoupper($pRange);
  
          // Extract range
          if (strpos($pRange, ':') === false) {
              $rangeA = $rangeB = $pRange;
          } else {
              list($rangeA, $rangeB) = explode(':', $pRange);
          }
  
          return [self::coordinateFromString($rangeA), self::coordinateFromString($rangeB)];
      }
docs: Calculate range boundaries.
  
  @param string $pRange Cell range (e.g. A1:A1)
  
  @return array Range coordinates [Start Cell, End Cell]
  where Start Cell and End Cell are arrays [Column ID, Row Number]