Tutorial for $_SERVER in Super Global Variables - scmGalaxy
A Sneak Peek into The $_SERVER in PHP
PHP $_SERVER | Working of $_ SERVER Function with Examples
PHP Cheat Sheet - Resources from GoSquared
What is a Referrer and how does it work? - Seobility Wiki
PHP Risanuri Hidayat, Ir., M.Sc.. Introduction What is PHP? –PHP stands for Hypertext Preprocessor –PHP is a server-side scripting language, like ASP. - ppt download
ajax - How I can get origin of request with PHP? - Stack Overflow