One of the biggest speed bottlenecks of sites today are images, specifically unoptimized images or large scaled images. With Apaches Rewrite module we can convert all existing jpegs and png files (and most gifs) to webp, then transparently rewrite them so that a request for img.png from a browser that supports webp will receive img.webp.
SetEnv, SetEnvIf, and SetEnvIfNoCase directives conditionally set environment variables accessible by scripts and apache based on HTTP Headers, Variables, and Request information.
Apache .htaccess and httpd.conf have the power to send and manipulate HTTP Header Requests like sending P3P privacy headers, Content-Type: UTF-8, Content-Language, etc. The power is immense and you can do some really cool stuff with HTTP Headers!