code: protected function determineHeaderTags($topLevel, $depth)
      {
          $desired = range((int) $topLevel, (int) $topLevel + ((int) $depth - 1));
          $allowed = [1, 2, 3, 4, 5, 6];
  
          return array_map(function($val) { return 'h'.$val; }, array_intersect($desired, $allowed));
      }
docs: Convert a topLevel and depth to H1..H6 tags array
  
  @param int $topLevel
  @param int $depth
  @return array|string[]  Array of header tags; ex: ['h1', 'h2', 'h3']