code: public function getColumn($pColumn)
      {
          $this->testColumnInRange($pColumn);
  
          if (!isset($this->columns[$pColumn])) {
              $this->columns[$pColumn] = new AutoFilter\Column($pColumn, $this);
          }
  
          return $this->columns[$pColumn];
      }
docs: Get a specified AutoFilter Column.
  
  @param string $pColumn Column name (e.g. A)
  
  @throws PhpSpreadsheetException
  
  @return AutoFilter\Column