code: public static function searchFiles($folder, $extension)
      {
          $scanResult = array();
          $result     = array();
          // Check if we have a file or folder.
          if (is_dir(TL_ROOT . '/' . $folder)) {
              $scanResult = scan(TL_ROOT . '/' . $folder);
          }
  
          // Run each value.
          foreach ($scanResult as $value) {
              if (!is_file(TL_ROOT . '/' . $folder . '/' . $value)) {
                  $result += self::searchFiles($folder . '/' . $value, $extension);
              } else {
                  if (preg_match('/'.$extension.'$/i', $value)) {
                      $result[$folder][$folder . '/' . $value] = $value;
                  }
              }
          }
  
          return $result;
      }
docs: Search all files with the given file extension below the given path.
  
  @param string $folder    The folder to scan.
  
  @param string $extension The file extension.
  
  @return array