code: public function setDiagonalDirection($pValue)
      {
          if ($pValue == '') {
              $pValue = self::DIAGONAL_NONE;
          }
          if ($this->isSupervisor) {
              $styleArray = $this->getStyleArray(['diagonalDirection' => $pValue]);
              $this->getActiveSheet()->getStyle($this->getSelectedCells())->applyFromArray($styleArray);
          } else {
              $this->diagonalDirection = $pValue;
          }
  
          return $this;
      }
docs: Set DiagonalDirection.
  
  @param int $pValue see self::DIAGONAL_*
  
  @return Borders