code: public static function absoluteCoordinate($pCoordinateString)
      {
          if (self::coordinateIsRange($pCoordinateString)) {
              throw new Exception('Cell coordinate string can not be a range of cells');
          }
  
          // Split out any worksheet name from the coordinate
          $worksheet = '';
          $cellAddress = explode('!', $pCoordinateString);
          if (count($cellAddress) > 1) {
              list($worksheet, $pCoordinateString) = $cellAddress;
          }
          if ($worksheet > '') {
              $worksheet .= '!';
          }
  
          // Create absolute coordinate
          list($column, $row) = self::coordinateFromString($pCoordinateString);
          $column = ltrim($column, '$');
          $row = ltrim($row, '$');
  
          return $worksheet . '$' . $column . '$' . $row;
      }
docs: Make string coordinate absolute.
  
  @param string $pCoordinateString e.g. 'A1'
  
  @throws Exception
  
  @return string Absolute coordinate        e.g. '$A$1'