Pat-On/php_demo_udemy

My questions:

Where to find PhP's functions implementation? How is implemented engine? How is implemented mechanism of communication between front and backend

Links from course:

https://www.php.net/download-docs.php

Super Globals

https://www.php.net/manual/en/language.variables.superglobals.php

Several predefined variables in PHP are "super-globals", which means they are available in all scopes throughout a script. There is no need to do global $variable; to access them within functions or methods.

    $GLOBALS
    $_SERVER
    $_GET
    $_POST
    $_FILES
    $_COOKIE
    $_SESSION
    $_REQUEST
    $_ENV