如何在标头中传递多个文件扩展名参数？

I have files of different extensions, So how can I define multiple extensions in one header. for example

 header("Content-type: application/xml"); 
 header("Content-type: application/txt");

Is there any possibilities are there, to define in a single header something like this

 header("Content-type: application/xml txt"); 

Thanks in advance for your suggestions

If you want in downloading any type of file you can just use application/octet-stream.

header('Content-Type: application/octet-stream');

// for example this will download any type of file

 header('Content-Description: File Transfer');
 header('Content-Type: application/octet-stream');
 header('Content-Disposition: attachment; filename="' . basename($file) . '"');
 header('Expires: 0');
 header('Cache-Control: must-revalidate');
 header('Pragma: public');
 header('Content-Length: ' . filesize($file));
 readfile($file);