code: protected function headerize($string)
      {
          $headers = preg_split("/[\\s,]+/", $string, -1, PREG_SPLIT_NO_EMPTY);
          $headers = array_map(function ($element) {
              return str_replace(' ', '-', ucwords(strtolower(str_replace(['_', '-'], [' ', ' '], $element))));
          }, $headers);
          return implode(', ', $headers);
      }
docs: Convert any string (including php headers with HTTP prefix) to header format like :
  * X-PINGOTHER -> X-Pingother
  * X_PINGOTHER -> X-Pingother
  @param string $string string to convert
  @return string the result in "header" format