To Specify a Vary: Accept-Encoding header in PHP

use this code copy and paste into your website root  ( .htaccess ) file


<IfModule mod_headers.c>
  <FilesMatch "\.(js|css|xml|gz)$">
    Header append Vary: Accept-Encoding
  </FilesMatch>
</IfModule>

and Check you any webpage in  Page Load Time Monitoring Tool   on  Pingdom Website. and see the difference  before Vary: Accept-Encoding header and now Vary: Accept-Encoding header .