HTTP Caching

https://betterexplained.com/articles/how-to-optimize-your-site-with-http-caching/

Using Expires Headers

ExpiresActive On
ExpiresDefault A0

# 1 YEAR - doesn't change often
<FilesMatch "\.(flv|ico|pdf|avi|mov|ppt|doc|mp3|wmv|wav)$">
ExpiresDefault A31536000
</FilesMatch>

# 1 WEEK - possible to be changed, unlikely
<FilesMatch "\.(jpg|jpeg|png|gif|swf)$">
ExpiresDefault A604800
</FilesMatch>

# 3 HOUR - core content, changes quickly
<FilesMatch "\.(txt|xml|js|css)$">
ExpiresDefault A10800
</FilesMatch>

Using max-age headers

# 1 YEAR
<FilesMatch "\.(flv|ico|pdf|avi|mov|ppt|doc|mp3|wmv|wav)$">
Header set Cache-Control "max-age=31536000, public"
</FilesMatch>

# 1 WEEK
<FilesMatch "\.(jpg|jpeg|png|gif|swf)$">
Header set Cache-Control "max-age=604800, public"
</FilesMatch>

# 3 HOUR
<FilesMatch "\.(txt|xml|js|css)$">
Header set Cache-Control "max-age=10800"
</FilesMatch>

# NEVER CACHE - notice the extra directives
<FilesMatch "\.(html|htm|php|cgi|pl)$">
Header set Cache-Control "max-age=0, private, no-store, no-cache, must-revalidate"
</FilesMatch>