code: public function getSharedComponent()
      {
          switch ($this->parentPropertyName) {
              case 'allBorders':
              case 'horizontal':
              case 'inside':
              case 'outline':
              case 'vertical':
                  throw new PhpSpreadsheetException('Cannot get shared component for a pseudo-border.');
  
                  break;
              case 'bottom':
                  return $this->parent->getSharedComponent()->getBottom();
              case 'diagonal':
                  return $this->parent->getSharedComponent()->getDiagonal();
              case 'left':
                  return $this->parent->getSharedComponent()->getLeft();
              case 'right':
                  return $this->parent->getSharedComponent()->getRight();
              case 'top':
                  return $this->parent->getSharedComponent()->getTop();
          }
      }
docs: Get the shared style component for the currently active cell in currently active sheet.
  Only used for style supervisor.
  
  @throws PhpSpreadsheetException
  
  @return Border