I have tried a tool to measure the speed of my web site. It is Pingdom https://tools.pingdom.com
There is an answer I do not understand "The following publicly cacheable, compressible resources should have a "Vary: Accept-Encoding" header: https://www.example.com/"
Can anyone explain what is that in a simple way and how can I improve it?
If I understand that is related to the way files are compressed. My server does not accept Gzip. It works well with deflate. I put that code in the .htaccess:
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/xml
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/x-javascript
It works well for Google page speed. But it seems that Pingdom still gives an error.