How do I read any request header in PHP

How should I read any header in PHP?

For example the custom header: X-Requested-With.

From stackoverflow

• $_SERVER['HTTP_X_REQUESTED_WITH']
  

• Google hit #1

  http://www.php.net/apache_request_headers

  <?php
  $headers = apache_request_headers();
  
  foreach ($headers as $header => $value) {
      echo "$header: $value <br />\n";
  }
  ?>
  

  See Also

  apache_response_headers() - Fetch all HTTP response headers

  alex : I assume this is only when using the Apache server... might need to let the OP know that :)

  Jacco : I was hoping he would do some reading for himself.