PHP Superglobals

The PHP engine uses a list of built-in variables that are accessible anywhere in a PHP script, called superglobals. These superglobals contain data that is mostly related to requests, but they also contain some server information and running PHP script file information as well.

The most frequently used superglobals are the $_SERVER, $_SESSION, $_GET, $_POST, $_COOKIE, and $_FILES variables.

A good practice is to not mess with superglobals across a project, meaning it would be better not to alter the existing data or to add more or remove data from these variables. Ideally, you would only access them once per request. $_SESSION is an exception in this matter, as its data is provided by the application and not by the PHP engine.

You can always learn about superglobals in more depth by visiting the official PHP documentation page, at http://php.net/manual/en/language.variables.superglobals.php.

$_SERVER

The $_SERVER superglobal contains request headers...