code: public function type($className)
      {
          if (!class_exists($className)) {
              throw new \InvalidArgumentException(
                  sprintf(
                      'Class %s is non-existent or could not be loaded',
                      $className
                  )
              );
          }
          $this->matrix[$this->currentRegion][] = $className;
  
          return $this;
      }
docs: Adds the type to the currently selected region.
  
  @param string $className
  
  @return ContentItemMatrix